3D semiconductor device and structure with metal layers

ABSTRACT

A semiconductor device, the device including: a first silicon layer including a first single crystal silicon; a first metal layer disposed over the first silicon layer; a second metal layer disposed over the first metal layer; a first level including a plurality of transistors, the first level disposed over the second metal layer, where the plurality of transistors include a second single crystal silicon; a third metal layer disposed over the first level; a fourth metal layer disposed over the third metal layer, where the fourth metal layer is aligned to the first metal layer with a less than 40 nm alignment error; and a via disposed through the first level, where the first level thickness is less than two microns.

This application is a continuation-in-part of U.S. patent applicationSer. No. 17/536,019, filed on Nov. 27, 2021, which is acontinuation-in-part of U.S. patent application Ser. No. 17/334,928,filed on May 31, 2021, now U.S. Pat. No. 11,217,565 issued on Jan. 4,2022, which is a continuation-in-part of U.S. patent application Ser.No. 17/195,517, filed on Mar. 8, 2021, now U.S. Pat. No. 11,063,024issued on Jul. 13, 2021, which is a continuation-in-part of U.S. patentapplication Ser. No. 17/020,766, filed on Sep. 14, 2020, now U.S. Pat.No. 11,018,116 issued on May 25, 2021, which is a continuation-in-partof U.S. patent application Ser. No. 16/683,244, filed on Nov. 13, 2019,now U.S. Pat. No. 10,811,395 issued on Oct. 20, 2020, which is acontinuation-in-part of U.S. patent application Ser. No. 16/409,840,filed on May 12, 2019, now U.S. Pat. No. 10,515,935 issued on Dec. 24,2019, which is a continuation-in-part of U.S. patent application Ser.No. 15/990,684, filed on May 28, 2018, now U.S. Pat. No. 10,297,580issued on May 21, 2019, which is a continuation-in-part of U.S. patentapplication Ser. No. 15/721,955, filed on Oct. 1, 2017, now U.S. Pat.No. 10,014,282 issued on Jul. 3, 2018, which is a continuation-in-partof U.S. patent application Ser. No. 15/008,444, filed on Jan. 28, 2016,now U.S. Pat. No. 9,786,636 issued on Oct. 10, 2017, which is acontinuation-in-part of U.S. patent application Ser. No. 14/541,452,filed on Nov. 14, 2014, now U.S. Pat. No. 9,252,134 issued on Feb. 2,2016, which is a continuation of U.S. patent application Ser. No.14/198,041, filed on Mar. 5, 2014, now U.S. Pat. No. 8,921,970 issued onDec. 30, 2014, which is a continuation of U.S. patent application Ser.No. 13/726,091, filed on Dec. 22, 2012, now U.S. Pat. No. 8,674,470issued on Mar. 18, 2014. The contents of the foregoing applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This application relates to the general field of Integrated Circuit (IC)devices and fabrication methods, and more particularly to multilayer orThree Dimensional Integrated Circuit (3D-IC) devices and fabricationmethods.

2. Discussion of Background Art

Over the past 40 years, there has been a dramatic increase infunctionality and performance of Integrated Circuits (ICs). This haslargely been due to the phenomenon of “scaling”; i.e., component sizeswithin ICs have been reduced (“scaled”) with every successive generationof technology. There are two main classes of components in ComplementaryMetal Oxide Semiconductor (CMOS) ICs, namely transistors and wires. With“scaling”, transistor performance and density typically improve and thishas contributed to the previously-mentioned increases in IC performanceand functionality. However, wires (interconnects) that connect togethertransistors degrade in performance with “scaling”. The situation todayis that wires dominate the performance, functionality and powerconsumption of ICs.

3D stacking of semiconductor devices or chips is one avenue to tacklethe wire issues. By arranging transistors in 3 dimensions instead of 2dimensions (as was the case in the 1990s), the transistors in ICs can beplaced closer to each other. This reduces wire lengths and keeps wiringdelay low.

There are many techniques to construct 3D stacked integrated circuits orchips including:

-   -   Monolithic 3D technology: With this approach, multiple layers of        transistors and wires can be monolithically constructed. Some        monolithic 3D and 3DIC approaches are described in U.S. Pat.        Nos. 8,273,610, 8,298,875, 8,362,482, 8,378,715, 8,379,458,        8,450,804, 8,557,632, 8,574,929, 8,581,349, 8,642,416,        8,669,778, 8,674,470, 8,687,399, 8,742,476, 8,803,206,        8,836,073, 8,902,663, 8,994,404, 9,023,688, 9,029,173,        9,030,858, 9,117,749, 9,142,553, 9,219,005, 9,385,058,        9,406,670, 9,460,978, 9,509,313, 9,640,531, 9,691,760,        9,711,407, 9,721,927, 9,799,761, 9,871,034, 9,953,870,        9,953,994, 10,014,292, 10,014,318, 10,515,981, 10,892,016; and        pending U.S. Patent Application Publications and applications,        Ser. Nos. 14/642,724, 15/150,395, 15/173,686, 16/337,665,        16/558,304, 16/649,660, 16/836,659, 17/151,867, 62/651,722;        62/681,249, 62/713,345, 62/770,751, 62/952,222, 62/824,288,        63/075,067, 63/091,307, 63/115,000, 63/220,443, 2021/0242189,        2020/0013791, 16/558,304; and PCT Applications (and        Publications): PCT/US2010/052093, PCT/US2011/042071        (WO2012/015550), PCT/US2016/52726 (WO2017053329),        PCT/US2017/052359 (WO2018/071143), PCT/US2018/016759        (WO2018144957), PCT/US2018/52332(WO 2019/060798), and        PCT/US2021/44110. The entire contents of the foregoing patents,        publications, and applications are incorporated herein by        reference.    -   Electro-Optics: There is also work done for integrated        monolithic 3D including layers of different crystals, such as        U.S. Pat. Nos. 8,283,215, 8,163,581, 8,753,913, 8,823,122,        9,197,804, 9,419,031, 9,941,319, 10,679,977, 10,943,934,        10,998,374, 11,063,071, and 11,133,344. The entire contents of        the foregoing patents, publications, and applications are        incorporated herein by reference.

An early work on monolithic 3D was presented in U.S. Pat. No. 7,052,941and follow-on work in related patents includes U.S. Pat. No. 7,470,598.A technique which has been used over the last 20 years to build SOIwafers, called “Smart-Cut” or “Ion-Cut”, was presented in U.S. Pat. No.7,470,598 as one of the options to perform layer transfer for theformation of a monolithic 3D device. Yet in a related patent disclosure,by the same inventor of U.S. Pat. No. 7,470,598, U.S. application Ser.No. 12/618,542 it states: “In one embodiment of the previous art,exfoliating implant method in which ion-implanting Hydrogen into thewafer surface is known. But this exfoliating implant method can destroylattice structure of the doped layer 400 by heavy ion-implanting. Inthis case, to recover the destroyed lattice structure, a long timethermal treatment in very high temperature is required. This longtime/high temperature thermal treatment can severely deform the celldevices of the lower region.” Moreover, in U.S. application Ser. No.12/635,496 by the same inventor is stated: [0034] Among the technologiesto form the detaching layer, one of the well-known technologies isHydrogen Exfoliating Implant. This method has a critical disadvantagewhich can destroy lattice structures of the substrate because it useshigh amount of ion implantation In order to recover the destroyedlattice structures, the substrate should be cured by heat treatment invery high temperature long time. This kind of high temperature heattreatment can damage cell devices in the lower regions.” Furthermore, inU.S. application Ser. No. 13/175,652 it is stated: “Among thetechnologies to form the detaching layer 207, one technology is calledas exfoliating implant in which gas phase ions such as hydrogen isimplanted to form the detaching layer, but in this technology, thecrystal lattice structure of the multiple doped layers 201, 203, 205 canbe damaged. In order to recover the crystal lattice damage, a thermaltreatment under very high temperature and longtime should be performed,and this can strongly damage the cell devices underneath.” In fact theInventor had posted a video infomercial on his corporate website, andwas up-loaded on YouTube on Jun. 1, 2011, clearly stating in referenceto the Smart Cut process: “The wafer bonding and detaching method iswell-known SOI or Semiconductor-On-Insulator technology. Compared toconventional bulk semiconductor substrates, SOI has been introduced toincrease transistor performance. However, it is not designed for 3D ICeither. Let me explain the reasons . . . . The dose of hydrogen is toohigh and, therefore, semiconductor crystalline lattices are demolishedby the hydrogen ion bombardment during the hydrogen ion implantation.Therefore, typically annealing at more than 1,100 Celsius is requiredfor curing the lattice damage after wafer detaching. Such hightemperature processing certainly destroys underlying devices andinterconnect layers. Without high temperature annealing, the transferredlayer should be the same as a highly defective amorphous layer. It seemsthat there is no way to cure the lattice damage at low temperatures.BeSang has disruptive 3D layer formation technology and it enablesformation of defect-free single crystalline semiconductor layer at lowtemperatures . . . ”

In at least one embodiment presented herein, an innovative method torepair the crystal lattice damage caused by the hydrogen implant isdescribed.

Regardless of the technique used to construct 3D stacked integratedcircuits or chips, heat removal is a serious issue for this technology.For example, when a layer of circuits with power density P is stackedatop another layer with power density P, the net power density is 2P.Removing the heat produced due to this power density is a significantchallenge. In addition, many heat producing regions in 3D stackedintegrated circuits or chips have a high thermal resistance to the heatsink, and this makes heat removal even more difficult.

Several solutions have been proposed to tackle this issue of heatremoval in 3D stacked integrated circuits and chips. These are describedin the following paragraphs.

Publications have suggested passing liquid coolant through multipledevice layers of a 3D-IC to remove heat. This is described in“Microchannel Cooled 3D Integrated Systems”, Proc. Intl. InterconnectTechnology Conference, 2008 by D. C. Sekar, et al., and “ForcedConvective Interlayer Cooling in Vertically Integrated Packages,” Proc.Intersoc. Conference on Thermal Management (ITHERM), 2008 by T.Brunschweiler, et al.

Thermal vias have been suggested as techniques to transfer heat fromstacked device layers to the heat sink. Use of power and ground vias forthermal conduction in 3D-ICs has also been suggested. These techniquesare described in “Allocating Power Ground Vias in 3D ICs forSimultaneous Power and Thermal Integrity” ACM Transactions on DesignAutomation of Electronic Systems (TODAES), May 2009 by Hao Yu, Joanna Hoand Lei He.

Other techniques to remove heat from 3D Integrated Circuits and Chipswill be beneficial.

Additionally the 3D technology according to some embodiments of theinvention may enable some very innovative IC alternatives with reduceddevelopment costs, increased yield, and other illustrative benefits.

SUMMARY

The invention may be directed to multilayer or Three DimensionalIntegrated Circuit (3D IC) devices and fabrication methods.

In one aspect, a semiconductor device, the device including: a firstsilicon layer including a first single crystal silicon; a first metallayer over the first silicon layer; a second metal layer over the firstmetal layer; a first level including a plurality of transistors over thesecond metal layer, where the plurality of transistors include a secondsingle crystal silicon; a third metal layer over the first level; afourth metal layer over the third metal layer, where the fourth metallayer is aligned to the first metal layer with less than 40 nm alignmenterror; and a via disposed through the first level, where the via has adiameter of less than 450 nm.

In another aspect, a semiconductor device, the device including: a firstsilicon layer including first single crystal silicon; a first metallayer over the first silicon layer; a second metal layer over the firstmetal layer; a first level including a plurality of transistors over thesecond metal layer, where the plurality of transistors include secondsingle crystal silicon; a third metal layer over the first level; afourth metal layer over the third metal layer, where the fourth metallayer is aligned to the first metal layer with less than 40 nm alignmenterror; and a via disposed through the first level, where the viaincludes tungsten.

In another aspect, a 3D semiconductor device, the device including: afirst level overlaid by a second level, the first level including firstcircuits, where the first circuits include single crystal firsttransistors and include first interconnections, where the second levelincludes second circuits, the second circuits include single crystalsecond transistors and include second interconnections, where the firstcircuit is aligned to the second circuit with less than 200 nmmisalignment; and a Global Power distribution network, where the firstlevel includes at least one Local Power distribution network, where theGlobal Power distribution network distributes power to the Local Powerdistribution network, where the Global Power distribution networkincludes wires including an at least 50% greater conductivity than wiresof the Local Power distribution network.

In another aspect, a semiconductor device, the device including: a firstsilicon layer including single crystal silicon; a first metal layer overthe first silicon layer; second metal layer over the first metal layer;a first level including a plurality of transistors over the second metallayer, where the plurality of transistors include single crystalsilicon; a third metal layer over the first level; a fourth metal layerover the third metal layer, where the fourth metal layer is aligned tothe first metal layer with less than 40 nm alignment error; a globalpower distribution network and a local power distribution network, wherethe global power distribution network includes the fourth metal layer,and where the local power distribution network includes the third metallayer.

In another aspect, a method to form a 3D semiconductor device, themethod including: providing a first level including first circuits, thefirst circuits including first transistors and first interconnection;preparing a second level including a silicon layer; forming secondcircuits over the second level, the second circuits including secondtransistors and second interconnection; transferring with bonding thesecond level on top of the first level; and then thinning the secondlevel to a thickness of less than ten microns, where the device includesan upper most semiconductor level, where the upper most semiconductorlevel includes Input/Output (“I/O”) circuits designed to connect thedevice to external devices, and where the bonding is hybrid bonding.

In another aspect, a method to form a 3D semiconductor device, themethod including: providing a first level including first circuits, thefirst circuits including first transistors and first interconnection;preparing a second level including a silicon layer; forming secondcircuits over the second level, the second circuits including secondtransistors and second interconnection; transferring with bonding thesecond level on top of the first level; and then thinning the secondlevel to a thickness of less than ten microns; and forming heat removalpaths designed to remove heat from the second circuits to an externalsurface of the 3D semiconductor device, where the bonding is hybridbonding.

In another aspect, a method to form a 3D semiconductor device, themethod including: providing a first level including first circuits, thefirst circuits including first transistors and first interconnection;preparing a second level including a silicon layer; forming secondcircuits over the second level, the second circuits including secondtransistors and second interconnection; transferring with bonding thesecond level on top of the first level; and then thinning the secondlevel to a thickness of less than thirty microns, where the bondingincludes oxide to oxide bonds, where the bonding includes metal to metalbonds, and where at least one of the metal to metal bond structures hasa pitch of less than 1 micron from another of the metal to metal bondstructures.

In another aspect, a method to form a 3D semiconductor device, themethod including: providing a first level including first circuits, thefirst circuits including first transistors and first interconnection;preparing a second level including a silicon layer; forming secondcircuits over the second level, the second circuits including secondtransistors and second interconnection; transferring with bonding thesecond level on top of the first level; and then thinning the secondlevel to a thickness of less than thirty microns, where the deviceincludes an upper most semiconductor level, where the upper mostsemiconductor level includes Input/Output (“I/O”) circuits designed toconnect the device to external devices, and where the bonding is hybridbonding.

In another aspect, a method to form a 3D semiconductor device, themethod including: providing a first level including first circuits, thefirst circuits including first transistors and first interconnection;preparing a second level including a silicon layer; forming secondcircuits over the second level, the second circuits including secondtransistors and second interconnection; transferring with bonding thesecond level on top of the first level; and then thinning the secondlevel to a thickness of less than thirty microns; and forming heatremoval paths designed to remove heat from the second circuits to anexternal surface of the 3D semiconductor device, where the bonding ishybrid bonding.

In another aspect, a semiconductor device, the device including: a firstsilicon layer including first single crystal silicon; a first metallayer disposed over the first silicon layer; a second metal layerdisposed over the first metal layer; a first level including a pluralityof transistors, the first level disposed over the second metal layer,where the plurality of transistors include second single crystalsilicon; a third metal layer disposed over the first level; a fourthmetal layer disposed over the third metal layer, where the fourth metallayer is aligned to the first metal layer with a less than 40 nmalignment error; a power distribution network, where the powerdistribution network includes the third metal layer, and a plurality ofconnection paths from the power distribution network to the plurality oftransistors.

In another aspect, a semiconductor device, the device including: a firstsilicon layer including first single crystal silicon; a first metallayer disposed over the first silicon layer; a second metal layerdisposed over the first metal layer; a first level including a pluralityof transistors, the first level disposed over the second metal layer,where the plurality of transistors include second single crystalsilicon; a third metal layer disposed over the first level; a fourthmetal layer disposed over the third metal layer, where the fourth metallayer is aligned to the first metal layer with a less than 40 nmalignment error; a via disposed through the first level; and connectionpads disposed over a portion of the fourth metal layer, where theconnection pads are capable to include connection to external devices.

In another aspect, a semiconductor device, the device including: a firstsilicon layer including a first single crystal silicon; a first metallayer disposed over the first silicon layer; a second metal layerdisposed over the first metal layer; a first level including a pluralityof transistors, the first level disposed over the second metal layer,where the plurality of transistors include a second single crystalsilicon; a third metal layer disposed over the first level; a fourthmetal layer disposed over the third metal layer, where the fourth metallayer is aligned to the first metal layer with a less than 40 nmalignment error; and a via disposed through the first level, where thefirst level thickness is less than two microns.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention will be understood and appreciatedmore fully from the following detailed description, taken in conjunctionwith the drawings in which:

FIG. 1 is an exemplary drawing illustration of a 3D integrated circuit;

FIG. 2 is an exemplary drawing illustration of another 3D integratedcircuit;

FIG. 3 is an exemplary drawing illustration of the power distributionnetwork of a 3D integrated circuit;

FIGS. 4A-4G are exemplary drawing illustrations of the integration of ashield/heat sink layer in a 3D-IC;

FIGS. 5A-5H are exemplary drawing illustrations of a process flow formanufacturing fully depleted MOSFET (FD-MOSFET) with an integratedshield/heat sink layer;

FIG. 6 shows a junction-less transistor as a switch for logicapplications (prior art);

FIGS. 7A-7M show a one-mask per layer 3D floating body DRAM;

FIGS. 8A-8J show a zero-mask per layer 3D resistive memory with ajunction-less transistor;

FIGS. 9A-9G show a zero-mask per layer 3D charge-trap memory;

FIGS. 10A-10B show periphery on top of memory layers;

FIGS. 11A-11E show polysilicon select devices for 3D memory andperipheral circuits at the bottom according to some embodiments of thecurrent invention;

FIGS. 12A-12F show polysilicon select devices for 3D memory andperipheral circuits at the top according to some embodiments of thecurrent invention.

DETAILED DESCRIPTION

Various embodiments of the invention are now described with reference tothe drawing figures. Persons of ordinary skill in the art willappreciate that the description and figures illustrate rather than limitthe invention and that in general the figures are not drawn to scale forclarity of presentation. Such skilled persons will also realize thatmany more embodiments are possible by applying the inventive principlescontained herein and that such embodiments fall within the scope of theinvention which is not to be limited except by the appended claims.

Some drawing figures may describe process flows for building devices.The process flows, which may be a sequence of steps for building adevice, may have many structures, numerals and labels that may be commonbetween two or more adjacent steps. In such cases, some labels, numeralsand structures used for a certain step's figure may have been describedin the previous steps' figures.

FIG. 1 illustrates a 3D integrated circuit. Two crystalline layers, 0104and 0116, which may include semiconductor materials such as, forexample, mono-crystalline silicon, germanium, GaAs, InP, and graphene,are shown. For this illustration, mono-crystalline (single crystal)silicon may be used. Silicon layer 0116 could be thinned down from itsoriginal thickness, and its final thickness could be in the range ofabout 0.01 um to about 50 um, for example, 10 nm, 100 nm, 200 nm, 0.4um, 1 um, 2 um or 5 um. Silicon layer 0104 could be thinned down fromits original thickness, and its final thickness could be in the range ofabout 0.01 um to about 50 um, for example, 10 nm, 100 nm, 200 nm, 0.4um, 1 um, 2 um or 5 um; however, due to strength considerations, siliconlayer 0104 may also be of thicknesses greater than 100 um, depending on,for example, the strength of bonding to heat removal apparatus 0102.Silicon layer 0104 may include transistors such as, for example,MOSFETS, FinFets, BJTs, HEMTs, HBTs, which may include gate electroderegion 0114, gate dielectric region 0112, source and drain junctionregions (not shown), and shallow trench isolation (STI) regions 0110.Silicon layer 0116 may include transistors such as, for example,MOSFETS, FinFets, BJTs, HEMTs, HBTs, which may include gate electroderegion 0134, gate dielectric region 0132, source and drain junctionregions (not shown), and shallow trench isolation (STI) regions 0130. Athrough-silicon via (TSV) 0118 could be present and may have anassociated surrounding dielectric region 0120. Wiring layers 0108 forsilicon layer 0104 and wiring dielectric regions 0106 may be present andmay form an associated interconnect layer or layers. Wiring layers 0138for silicon layer 0116 and wiring dielectric 0136 may be present and mayform an associated interconnect layer or layers. Through-silicon via(TSV) 0118 may connect to wiring layers 0108 and wiring layers 0138 (notshown). The heat removal apparatus 0102 may include a heat spreaderand/or a heat sink. The heat removal problem for the 3D integratedcircuit shown in FIG. 1 is immediately apparent. The silicon layer 0116is far away from the heat removal apparatus 0102, and it may bedifficult to transfer heat among silicon layer 0116 and heat removalapparatus 0102. Furthermore, wiring dielectric regions 0106 may notconduct heat well, and this increases the thermal resistance amongsilicon layer 0116 and heat removal apparatus 0102. Silicon layer 0104and silicon layer 0116 may be may be substantially absent ofsemiconductor dopants to form an undoped silicon region or layer, ordoped, such as, for example, with elemental or compound species thatform a p+, or p, or p−, or n+, or n, or n− silicon layer or region. Theheat removal apparatus 0102 may include an external surface from whichheat transfer may take place by methods such as air cooling, liquidcooling, or attachment to another heat sink or heat spreader structure.

FIG. 2 illustrates an exemplary 3D integrated circuit that could beconstructed, for example, using techniques described in U.S. Pat. Nos.8,273,610, 8,557,632, and 8,581,349. The contents of the foregoingpatent and applications are incorporated herein by reference. Twocrystalline layers, 0204 and 0216, which may include semiconductormaterials such as, for example, mono-crystalline silicon, germanium,GaAs, InP, and graphene, are shown. For this illustration,mono-crystalline (single crystal) silicon may be used. Silicon layer0216 could be thinned down from its original thickness, and its finalthickness could be in the range of about 0.01 um to about 50 um, forexample, 10 nm, 100 nm, 200 nm, 0.4 um, 1 um, 2 um or 5 um. Siliconlayer 0204 could be thinned down from its original thickness, and itsfinal thickness could be in the range of about 0.01 um to about 50 um,for example, 10 nm, 100 nm, 200 nm, 0.4 um, 1 um, 2 um or 5 um; however,due to strength considerations, silicon layer 0204 may also be ofthicknesses greater than 100 um, depending on, for example, the strengthof bonding to heat removal apparatus 0202. Silicon layer 0204 mayinclude transistors such as, for example, MOSFETS, FinFets, BJTs, HEMTs,HBTs, which may include gate electrode region 0214, gate dielectricregion 0212, source and drain junction regions (not shown for clarity)and shallow trench isolation (STI) regions 0210. Silicon layer 0216 mayinclude transistors such as, for example, MOSFETS, FinFets, BJTs, HEMTs,HBTs, which may include gate electrode region 0234, gate dielectricregion 0232, source and drain junction regions (not shown for clarity),and shallow trench isolation (STI) regions 0222. It can be observed thatthe STI regions 0222 can go right through to the bottom of silicon layer0216 and provide good electrical isolation. This, however, may causechallenges for heat removal from the STI surrounded transistors sinceSTI regions 0222 are typically composed of insulators that do notconduct heat well. Therefore, the heat spreading capabilities of siliconlayer 0216 with STI regions 0222 are low. A through-layer via (TLV) 0218may be present and may include an associated surrounding dielectricregion 0220. Wiring layers 0208 for silicon layer 0204 and wiringdielectric regions 0206 may be present and may form an associatedinterconnect layer or layers. Wiring layers 0238 for silicon layer 0216and wiring dielectric 0236 may be present and may form an associatedinterconnect layer or layers. Through-layer via (TLV) 0218 may connectto wiring layers 0208 and wiring layers 0238 (not shown). The heatremoval apparatus 0202 may include a heat spreader and/or a heat sink.The heat removal problem for the 3D integrated circuit shown in FIG. 2is immediately apparent. The silicon layer 0216 may be far away from theheat removal apparatus 0202, and it may be difficult to transfer heatamong silicon layer 0216 and heat removal apparatus 0202. Furthermore,wiring dielectric regions 0206 may not conduct heat well, and thisincreases the thermal resistance among silicon layer 0216 and heatremoval apparatus 0202. The heat removal challenge is furtherexacerbated by the poor heat spreading properties of silicon layer 0216with STI regions 0222. Silicon layer 0204 and silicon layer 0216 may bemay be substantially absent of semiconductor dopants to form an undopedsilicon region or layer, or doped, such as, for example, with elementalor compound species that form a p+, or p, or p−, or n+, or n, or n−silicon layer or region. The heat removal apparatus 0202 may include anexternal surface from which heat transfer may take place by methods suchas air cooling, liquid cooling, or attachment to another heat sink orheat spreader structure.

FIG. 3 illustrates how the power or ground distribution network of a 3Dintegrated circuit could assist heat removal. FIG. 3 illustrates anexemplary power distribution network or structure of the 3D integratedcircuit. As shown in FIGS. 1 and 2, a 3D integrated circuit, could, forexample, be constructed with two silicon layers, first silicon layer0304 and second silicon layer 0316. The heat removal apparatus 0302could include, for example, a heat spreader and/or a heat sink. Thepower distribution network or structure could consist of a global powergrid 0310 that takes the supply voltage (denoted as V_(DD)) from thechip/circuit power pads and transfers V_(DD) to second local power grid0308 and first local power grid 0306, which transfers the supply voltageto logic/memory cells, transistors, and/or gates such as secondtransistor 0314 and first transistor 0315. Second layer vias 0318 andfirst layer vias 0312, such as the previously described TSV or TLV,could be used to transfer the supply voltage from the global power grid0310 to second local power grid 0308 and first local power grid 0306.The global power grid 0310 may also be present among first silicon layer0304 and second silicon layer 0316. The 3D integrated circuit could havea similarly designed and laid-out distribution networks, such as forground and other supply voltages, as well. The power grid may bedesigned and constructed such that each layer or strata of transistorsand devices may be supplied with a different value Vdd. For example,first silicon layer 0304 may be supplied by its power grid to have a Vddvalue of 1.0 volts and second silicon layer 0316 a Vdd value of 0.8volts. Furthermore, the global power grid 0310 wires may be constructedwith substantially higher conductivity, for example 30% higher, 50%higher, 2× higher, than local power grids, for example, such as firstlocal power grid 0306 wires and second local power grid 0308 wires. Thethickness, linewidth, and material composition for the global power grid0310 wires may provide for the higher conductivity, for example, thethickness of the global power grid 0310 wires may be twice that of thelocal power grid wires and/or the linewidth of the global power grid0310 wires may be 2× that of the local power grid wires. Moreover, theglobal power grid 0310 may be optimally located in the top strata orlayer of transistors and devices.

Typically, many contacts may be made among the supply and grounddistribution networks and first silicon layer 0304. Due to this, therecould exist a low thermal resistance among the power/ground distributionnetwork and the heat removal apparatus 0302. Since power/grounddistribution networks may be typically constructed of conductive metalsand could have low effective electrical resistance, the power/grounddistribution networks could have a low thermal resistance as well. Eachlogic/memory cell or gate on the 3D integrated circuit (such as, forexample, second transistor 0314) is typically connected to V_(DD) andground, and therefore could have contacts to the power and grounddistribution network. The contacts could help transfer heat efficiently(for example, with low thermal resistance) from each logic/memory cellor gate on the 3D integrated circuit (such as, for example, secondtransistor 0314) to the heat removal apparatus 0302 through thepower/ground distribution network and the silicon layer 0304. Siliconlayer 0304 and silicon layer 0316 may be may be substantially absent ofsemiconductor dopants to form an undoped silicon region or layer, ordoped, such as, for example, with elemental or compound species thatform a p+, or p, or p−, or n+, or n, or n− silicon layer or region. Theheat removal apparatus 0302 may include an external surface from whichheat transfer may take place by methods such as air cooling, liquidcooling, or attachment to another heat sink or heat spreader structure.

Defect annealing, such as furnace thermal or optical annealing, of thinlayers of the crystalline materials generally included in 3D-ICs to thetemperatures that may lead to substantial dopant activation or defectanneal, for example above 600° C., may damage or melt the underlyingmetal interconnect layers of the stacked 3D-IC, such as copper oraluminum interconnect layers. An embodiment of the invention is to form3D-IC structures and devices wherein a heat spreading, heat conductingand/or optically reflecting or absorbent material layer or layers (whichmay be called a shield) is incorporated between the sensitive metalinterconnect layers and the layer or regions being optically irradiatedand annealed, or annealed from the top of the 3D-IC stack using othermethods. An exemplary generalized process flow is shown in FIGS. 4A-F.An exemplary process flow for a FD-MOSFET with an optional integratedheat shield/spreader is shown in FIGS. 5A-5H. The 3D-ICs may beconstructed in a 3D stacked layer using procedures outlined herein (suchas, for example, FIGS. 39, 40, 41 of parent now U.S. Pat. No. 8,674,470)and in U.S. Pat. Nos. 8,273,610 and 8,557,632 and 8,581,349. Thecontents of the foregoing applications are incorporated herein byreference. The topside defect anneal may include optical annealing torepair defects in the crystalline 3D-IC layers and regions (which may becaused by the ion-cut implantation process), and may be utilized toactivate semiconductor dopants in the crystalline layers or regions of a3D-IC, such as, for example, LDD, halo, source/drain implants. The 3D-ICmay include, for example, stacks formed in a monolithic manner with thinlayers or stacks and vertical connection such as TLVs, and stacks formedin an assembly manner with thick (>2 um) layers or stacks and verticalconnections such as TSVs. Optical annealing beams or systems, such as,for example, a laser-spike anneal beam from a commercial semiconductormaterial oriented single or dual-beam continuous wave (CW) laser spikeanneal DB-LSA system of Ultratech Inc., San Jose, Calif., USA (10.6 umlaser wavelength), or a short pulse laser (such as 160 ns), with 308 nmwavelength, and large area (die or step-field sized, including 1 cm²)irradiation such as offered by Excico of Gennevilliers, France, may beutilized (for example, see Huet, K., “Ultra Low Thermal Budget LaserThermal Annealing for 3D Semiconductor and Photovoltaic Applications,”NCCAVS 2012 Junction Technology Group, Semicon West, San Francisco, Jul.12, 2012). Additionally, the defect anneal may include, for example,laser anneals (such as suggested in Rajendran, B., “Sequential 3D ICFabrication: Challenges and Prospects”, Proceedings of VLSI Multi LevelInterconnect Conference 2006, pp. 57-64), Ultrasound Treatments (UST),megasonic treatments, and/or microwave treatments. The topside defectanneal ambient may include, for example, vacuum, high pressure (greaterthan about 760 torr), oxidizing atmospheres (such as oxygen or partialpressure oxygen), and/or reducing atmospheres (such as nitrogen orargon). The topside defect anneal may include temperatures of the layerbeing annealed above about 400° C. (a high temperature thermal anneal),including, for example, 600° C., 800° C., 900° C., 1000° C., 1050° C.,1100° C. and/or 1120° C., and the sensitive metal interconnect (forexample, may be copper or aluminum containing) and/or device layersbelow may not be damaged by the annealing process, for example, whichmay include sustained temperatures that do not exceed 200° C., exceed300° C., exceed 370° C., or exceed 400° C. As understood by those ofordinary skill in the art, short-timescale (nanosceonds to miliseconds)temperatures above 400° C. may also be acceptable for damage avoidance,depending on the acceptor layer interconnect metal systems used. Thetopside defect anneal may include activation of semiconductor dopants,such as, for example, ion implanted dopants or PLAD applied dopants. Itwill also be understood by one of ordinary skill in the art that themethods, such as the heat sink/shield layer and/or use of short pulseand short wavelength optical anneals, may allow almost any type oftransistor, for example, such as FinFets, bipolar, nanowire transistors,to be constructed in a monolithic 3D fashion as the thermal limit ofdamage to the underlying metal interconnect systems is overcome.Moreover, multiple pulses of the laser, other optical annealingtechniques, or other anneal treatments such as microwave, may beutilized to improve the anneal, activation, and yield of the process.The transistors formed as described herein may include many types ofmaterials; for example, the channel and/or source and drain may includesingle crystal materials such as silicon, germanium, or compoundsemiconductors such as GaAs, InP, GaN, SiGe, and although the structuresmay be doped with the tailored dopants and concentrations, they maystill be substantially crystalline or mono-crystalline.

As illustrated in FIG. 4A, a generalized process flow may begin with adonor wafer 400 that may be preprocessed with wafer sized layers 402 ofconducting, semi-conducting or insulating materials that may be formedby deposition, ion implantation and anneal, oxidation, epitaxial growth,combinations of above, or other semiconductor processing steps andmethods. For example, donor wafer 400 and wafer sized layers 402 mayinclude semiconductor materials such as, for example, mono-crystallinesilicon, germanium, GaAs, InP, and graphene. For this illustration,mono-crystalline (single crystal) silicon and associated siliconoriented processing may be used. The donor wafer 400 may be preprocessedwith a layer transfer demarcation plane (shown as dashed line) 499, suchas, for example, a hydrogen implant cleave plane, before or after(typical) wafer sized layers 402 are formed. Layer transfer demarcationplane 499 may alternatively be formed within wafer sized layers 402.Other layer transfer processes, some described in the referenced patentdocuments, may alternatively be utilized. Damage/defects to thecrystalline structure of donor wafer 400 may be annealed by some of theannealing methods described, for example the short wavelength pulsedlaser techniques, wherein the donor wafer 400 wafer sized layers 402 andportions of donor wafer 400 may be heated to defect annealingtemperatures, but the layer transfer demarcation plane 499 may be keptbelow the temperate for cleaving and/or significant hydrogen diffusion.Dopants in at least a portion of wafer sized layers 402 may also beelectrically activated. Thru the processing, donor wafer 400 and/orwafer sized layers 402 could be thinned from its original thickness, andtheir/its final thickness could be in the range of about 0.01 um toabout 50 um, for example, 10 nm, 100 nm, 200 nm, 0.4 um, 1 um, 2 um or 5um. Donor wafer 400 and wafer sized layers 402 may include preparatorylayers for the formation of horizontally or vertically oriented types oftransistors such as, for example, MOSFETS, FinFets, FD-RCATs, BJTs,HEMTs, HBTs, JFETs, JLTs, or partially processed transistors (forexample, the replacement gate HKMG process described in the referencedpatent documents). Donor wafer 400 and wafer sized layers 402 mayinclude the layer transfer devices and/or layer or layers containedherein this document or referenced patent documents, for example, DRAMSi/SiO₂ layers, RCAT doped layers, multi-layer doped structures, orstarting material doped or undoped monocrystalline silicon, orpolycrystalline silicon. Donor wafer 400 and wafer sized layers 402 mayhave alignment marks (not shown). Acceptor wafer 410 may be apreprocessed wafer, for example, including monocrystalline bulk siliconor SOI, that may have fully functional circuitry including metal layers(including aluminum or copper metal interconnect layers that may connectacceptor wafer 410 transistors and metal structures, such as TLV landingstrips and pads, prepared to connect to the transferred layer devices)or may be a wafer with previously transferred layers, or may be a blankcarrier or holder wafer, or other kinds of substrates suitable for layertransfer processing. Acceptor wafer 410 may have alignment marks 490 andmetal connect pads or strips 480 and ray blocked metal interconnect 481.Acceptor wafer 410 may include transistors such as, for example,MOSFETS, FinFets, FD-RCATs, BJTs, JFETs, JLTs, HEMTs, and/or HBTs.Acceptor wafer 410 may include shield/heat sink layer 488, which mayinclude materials such as, for example, Aluminum, Tungsten (a refractorymetal), Copper, silicon or cobalt based silicides, or forms of carbonsuch as carbon nanotubes or DLC (Diamond Like Carbon). Shield/heat sinklayer 488 may have a thickness range of about 50 nm to about 1 mm, forexample, 50 nm, 100 nm, 200 nm, 300 nm, 500 nm, 0.1 um, 1 um, 2 um, and10 um. Shield/heat sink layer 488 may include isolation openings 486,and alignment mark openings 487, which may be utilized for shortwavelength alignment of top layer (donor) processing to the acceptorwafer alignment marks 490. Shield/heat sink layer 488 may include shieldpath connect 485 and shield path via 483. Shield path via 483 maythermally and/or electrically couple and connect shield path connect 485to acceptor wafer 410 interconnect metallization layers such as, forexample, metal connect pads or strips 480 (shown). If two shield/heatsink layers 488 are utilized, one on top of the other and separated byan isolation layer common in semiconductor BEOL, such as carbon dopedsilicon oxide, shield path connect 485 may also thermally and/orelectrically couple and connect each shield/heat sink layer 488 to theother and to acceptor wafer 410 interconnect metallization layers suchas, for example, metal connect pads or strips 480, thereby creating aheat conduction path from the shield/heat sink layer 488 to the acceptorwafer substrate, and a heat sink (shown in FIG. 4F). The topmostshield/heat sink layer may include a higher melting point material, forexample a refractory metal such as Tungsten, and the lower heat shieldlayer may include a lower melting point material such as copper.

As illustrated in FIG. 4B, two exemplary top views of shield/heat sinklayer 488 are shown. In shield/heat sink portion 420 a shield area 422of the shield/heat sink layer 488 materials described above and in theincorporated references may include TLV/TSV connects 424 and isolationopenings 486. Isolation openings 486 may be the absence of the materialof shield area 422. TLV/TSV connects 424 are an example of a shield pathconnect 485. TLV/TSV connects 424 and isolation openings 486 may bedrawn in the database of the 3D-IC stack and may formed during theacceptor wafer 410 processing. In shield/heat sink portion 430 a shieldarea 432 of the shield/heat sink layer 488 materials described above andin the incorporated references may have metal interconnect strips 434and isolation openings 486. Metal interconnect strips 434 may besurrounded by regions, such as isolation openings 486, where thematerial of shield area 432 may be etched away, thereby stoppingelectrical conduction from metal interconnect strips 434 to shield area432 and to other metal interconnect strips. Metal interconnect strips434 may be utilized to connect/couple the transistors formed in thedonor wafer layers, such as 402, to themselves from the ‘backside’ or‘underside’ and/or to transistors in the acceptor wafer level/layer.Metal interconnect strips 434 and shield/heat sink layer 488 regionssuch as shield area 422 and shield area 432 may be utilized as a groundplane for the transistors above it residing in the donor wafer layer orlayers and/or may be utilized as power supply or back-bias, such as Vddor Vsb, for the transistors above it residing in the transferred donorwafer layer or layers. The strips and/or regions of shield/heat sinklayer 488 may be controlled by second layer transistors when supplyingpower or other signals such as data or control. For example, asillustrated in FIG. 4G, the topmost shield/heat sink layer 488 mayinclude a topmost shield/heat sink portion 470, which may be configuredas fingers or stripes of conductive material, such as top strips 474 andstrip isolation spaces 476, which may be utilized, for example, toprovide back-bias, power, or ground to the second layer transistorsabove it residing in the donor wafer layer or layers (for example donorwafer device structures 450). A second shield/heat sink layer 488, belowthe topmost shield/heat sink layer, may include a second shield/heatsink portion 472, which may be configured as fingers or stripes ofconductive material, such as second strips 478 and strip isolationspaces 476, may be oriented in a different direction (although notnecessarily so) than the topmost strips, and may be utilized, forexample, to provide back-bias, power, or ground to the second layertransistors above it residing in the donor wafer layer or layers (forexample donor wafer device structures 450). Openings, such as opening479, in the topmost shield/heat sink layer may be designed to allowconnection from the second layer of transistors to the secondshield/heat sink layer, such as from donor wafer device structures 450to second strips 478. The strips or fingers may be illustrated asorthogonally oriented layer to layer, but may also take other drawnshapes and forms; for example, such as diagonal running shapes as in theX-architecture, overlapping parallel strips, and so on. The portions ofthe shield/heat sink layer 488 or layers may include a combination ofthe strip/finger shapes of FIG. 4G and the illustrated via connects andfill-in regions of FIG. 4B.

Bonding surfaces, donor bonding surface 401 and acceptor bonding surface411, may be prepared for wafer bonding by depositions (such as siliconoxide), polishes, plasma, or wet chemistry treatments to facilitatesuccessful wafer to wafer bonding. The insulation layer, such asdeposited bonding oxides and/or before bonding preparation existingoxides, between the donor wafer transferred layer and the acceptor wafertopmost metal layer, may include thicknesses of less than 1 um, lessthan 500 nm, less than 400 nm, less than 300 nm, less than 200 nm, orless than 100 nm.

As illustrated in FIG. 4C, the donor wafer 400 with wafer sized layers402 and layer transfer demarcation plane 499 may be flipped over,aligned, and bonded to the acceptor wafer 410. The donor wafer 400 withwafer sized layers 402 may have alignment marks (not shown). Varioustopside defect anneals may be utilized. For this illustration, anoptical beam such as the laser annealing previously described is used.Optical anneal beams may be optimized to focus light absorption and heatgeneration at or near the layer transfer demarcation plane (shown asdashed line) 499 to provide a hydrogen bubble cleave with exemplarycleave ray 451. The laser assisted hydrogen bubble cleave with theabsorbed heat generated by exemplary cleave ray 451 may also include apre-heat of the bonded stack to, for example, about 100° C. to about400° C., and/or a thermal rapid spike to temperatures above about 200°C. to about 600° C. The laser assisted ion-cut cleave may provide asmoother cleave surface upon which better quality transistors may bemanufactured. Reflected ray 453 may be reflected and/or absorbed byshield/heat sink layer 488 regions thus blocking the optical absorptionof ray blocked metal interconnect 481 and potentially enhancing theefficiency of optical energy absorption of the wafer sized layers 402.Additionally, shield/heat sink layer 488 may laterally spread andconduct the heat generated by the topside defect anneal, and inconjunction with the dielectric materials (low heat conductivity) aboveand below shield/heat sink layer 488, keep the interconnect metals andlow-k dielectrics of the acceptor wafer interconnect layers cooler thana damage temperature, such as, for example, 400° C. Annealing of dopantsor annealing of damage, such as from the H cleave implant damage, may beaccomplished by optical annealing rays, such as repair ray 455. A smallportion of the optical energy, such as unblocked ray 457, may hit andheat, or be reflected, by (a few rays as the area of the heat shieldopenings, such as 424, is small compared to the die or device area) suchas metal connect pads or strips 480. Heat generated by absorbed photonsfrom, for example, cleave ray 451, reflected ray 453, and/or repair ray455 may also be absorbed by shield/heat sink layer 488 regions anddissipated laterally and may keep the temperature of underlying metallayers, such as ray blocked metal interconnect 481, and other metallayers below it, cooler and prevent damage. Shield/heat sink layer 488may act as a heat spreader. A second layer of shield/heat sink layer 488(not shown) may have been constructed (during the acceptor wafer 410formation) with a low heat conductive material sandwiched between thetwo heat sink layers, such as silicon oxide or carbon doped ‘low-k’silicon oxides, for improved thermal protection of the acceptor waferinterconnect layers, metal and dielectrics. Electrically conductivematerials may be used for the two layers of shield/heat sink layer 488and thus may provide, for example, a Vss and a Vdd plane for powerdelivery that may be connected to the donor layer transistors above, aswell may be connected to the acceptor wafer transistors below.Shield/heat sink layer 488 may include materials with a high thermalconductivity greater than 10 W/m-K, for example, copper (about 400W/m-K), aluminum (about 237 W/m-K), Tungsten (about 173 W/m-K), PlasmaEnhanced Chemical Vapor Deposited Diamond Like Carbon-PECVD DLC (about1000 W/m-K), and Chemical Vapor Deposited (CVD) graphene (about 5000W/m-K). Shield/heat sink layer 488 may be sandwiched and/orsubstantially enclosed by materials with a low thermal conductivity lessthan 10 W/m-K, for example, silicon dioxide (about 1.4 W/m-K). Thesandwiching of high and low thermal conductivity materials in layers,such as shield/heat sink layer 488 and under & overlying dielectriclayers, spreads the localized heat/light energy of the topside anneallaterally and protect the underlying layers of interconnectmetallization & dielectrics, such as in the acceptor wafer, from harmfultemperatures or damage. Further, absorber layers or regions, forexample, including amorphous carbon, amorphous silicon, and phasechanging materials (see U.S. Pat. Nos. 6,635,588 and 6,479,821 toHawryluk et al. for example), may be utilized to increase the efficiencyof the optical energy capture in conversion to heat for the desiredannealing or activation processes. For example, pre-processed layers 402may include a layer or region of optical absorbers such as transferredabsorber region 475, acceptor wafer 410 may include a layer or region ofoptical absorbers such as acceptor absorber region 473, and seconddevice layer 405 may include a layer or region of optical absorbers suchas post transfer absorber regions 477 (shown in FIG. 4E). Transferredabsorber region 475, acceptor absorber region 473, and/or post transferabsorber regions 477 may be permanent (could be found within the devicewhen manufacturing is complete) or temporary so is removed during themanufacturing process.

As illustrated in FIG. 4D, the donor wafer 400 may be cleaved at orthinned to (or past, not shown) the layer transfer demarcation plane499, leaving donor wafer portion 403 and the pre-processed layers 402bonded to the acceptor wafer 410, by methods such as, for example,ion-cut or other layer transfer methods. The layer transfer demarcationplane 499 may instead be placed in the pre-processed layers 402. Opticalanneal beams, in conjunction with reflecting layers and regions andabsorbing enhancement layers and regions, may be optimized to focuslight absorption and heat generation within or at the surface of donorwafer portion 403 and provide surface smoothing and/or defect annealing(defects may be from the cleave and/or the ion-cut implantation), and/orpost ion-implant dopant activation with exemplary smoothing/annealingray 466. The laser assisted smoothing/annealing with the absorbed heatgenerated by exemplary smoothing/annealing ray 466 may also include apre-heat of the bonded stack to, for example, about 100° C. to about400° C., and/or a thermal rapid spike to temperatures above about 200°C. to about 600° C. Moreover, multiple pulses of the laser may beutilized to improve the anneal, activation, and yield of the process.Reflected ray 463 may be reflected and/or absorbed by shield/heat sinklayer 488 regions thus blocking the optical absorption of ray blockedmetal interconnect 481. Annealing of dopants or annealing of damage,such as from the H cleave implant damage, may be also accomplished by aset of rays such as repair ray 465. A small portion of the opticalenergy, such as unblocked ray 467, may hit and heat, or be reflected, bya few rays (as the area of the heat shield openings, such as 424, issmall) such as metal connect pads or strips 480. Heat generated byabsorbed photons from, for example, smoothing/annealing ray 466,reflected ray 463, and/or repair ray 465 may also be absorbed byshield/heat sink layer 488 regions and dissipated laterally and may keepthe temperature of underlying metal layers, such as ray blocked metalinterconnect 481, and other metal layers below it, cooler and preventdamage. A second layer of shield/heat sink layer 488 may be constructedwith a low heat conductive material sandwiched between the two heat sinklayers, such as silicon oxide or carbon doped ‘low-k’silicon oxides, forimproved thermal protection of the acceptor wafer interconnect layers,metal and dielectrics. Shield/heat sink layer 488 may act as a heatspreader. When there may be more than one shield/heat sink layer 488 inthe device, the heat conducting layer closest to the second crystallinelayer may be constructed with a different material, for example a highmelting point material, for example a refractory metal such as tungsten,than the other heat conducting layer or layers, which may be constructedwith, for example, a lower melting point material such as aluminum orcopper. Electrically conductive materials may be used for the two layersof shield/heat sink layer 488 and thus may provide, for example, a Vssand a Vdd plane that may be connected to the donor layer transistorsabove, as well may be connected to the acceptor wafer transistors below.Furthermore, some or all of the layers utilized as shield/heat sinklayer 488, which may include shapes of material such as the strips orfingers as illustrated in FIG. 4G, may be driven by a portion of thesecond layer transistors and circuits (within the transferred donorwafer layer or layers) or the acceptor wafer transistors and circuits,to provide a programmable back-bias to at least a portion of the secondlayer transistors. The programmable back bias may utilize a circuit todo so, for example, such as shown in FIG. 17B of U.S. Pat. No.8,273,610, the contents incorporated herein by reference; wherein the‘Primary’ layer may be the second layer of transistors for which theback-bias is being provided, the ‘Foundation’ layer could be either thesecond layer transistors (donor) or first layer transistors (acceptor),and the routing metal lines connections 1723 and 1724 may includeportions of the shield/heat sink layer 488 layer or layers. Moreover,some or all of the layers utilized as shield/heat sink layer 488, whichmay include strips or fingers as illustrated in FIG. 4G, may be drivenby a portion of the second layer transistors and circuits (within thetransferred donor wafer layer or layers) or the acceptor wafertransistors and circuits to provide a programmable power supply to atleast a portion of the second layer transistors. The programmable powersupply may utilize a circuit to do so, for example, such as shown inFIG. 17C of U.S. Pat. No. 8,273,610, the contents incorporated herein byreference; wherein the ‘Primary’ layer may be the second layer oftransistors for which the programmable power supplies are being providedto, the ‘Foundation’ layer could be either the second layer transistors(donor) or first layer transistors (acceptor), and the routing metalline connections from Vout to the various second layer transistors mayinclude portions of the shield/heat sink layer 488 layer or layers. TheVsupply on line 17C12 and the control signals on control line 17C16 maybe controlled by and/or generated in the second layer transistors(donor, for example donor wafer device structures 450) or first layertransistors (acceptor, for example acceptor wafer transistors anddevices 493), or off chip circuits. Furthermore, some or all of thelayers utilized as shield/heat sink layer 488, which may include stripsor fingers as illustrated in FIG. 4G or other shapes such as those inFIG. 4B, may be utilized to distribute independent power supplies tovarious portions of the second layer transistors (donor, for exampledonor wafer device structures 450) or first layer transistors (acceptor,for example acceptor wafer transistors and devices 493) and circuits;for example, one power supply and/or voltage may be routed to thesequential logic circuits of the second layer and a different powersupply and/or voltage routed to the combinatorial logic circuits of thesecond layer. Patterning of shield/heat sink layer 488 or layers canimpact their heat-shielding capacity. This impact may be mitigated, forexample, by enhancing the top shield/heat sink layer 488 areal density,creating more of the secondary shield/heat sink layers 488, or attendingto special CAD rules regarding their metal density, similar to CAD rulesthat are required to accommodate Chemical-Mechanical Planarization(CMP). These constraints would be integrated into a design and layoutEDA tool.

As illustrated in FIG. 4E, the remaining donor wafer portion 403 may beremoved by polishing or etching and the transferred layers 402 may befurther processed to create second device layer 405 which may includedonor wafer device structures 450 and metal interconnect layers (such assecond device layer metal interconnect 461) that may be preciselyaligned to the acceptor wafer alignment marks 490. Donor wafer devicestructures 450 may include, for example, CMOS transistors such as N typeand P type transistors, or at least any of the other transistor ordevice types discussed herein this document or referenced patentdocuments. The details of CMOS in one transferred layer and theorthogonal connect strip methodology may be found as illustrated in atleast FIGS. 30-4, 73-80, and 94 and related specification sections ofU.S. Pat. No. 8,273,610. As discussed above and herein this document andreferenced patent documents, annealing of dopants or annealing ofdamage, such as from the dopant application such as ion-implantation, orfrom etch processes during the formation of the transferred layertransistor and device structures, may be accomplished by opticalannealing. Donor wafer device structures 450 may include transistorsand/or semiconductor regions wherein the dopant concentration of theregions in the horizontal plane, such as shown as exemplary dopant plane449, may have regions that differ substantially in dopant concentration,for example, 10× greater, and/or may have a different dopant type, suchas, for example p-type or n-type dopant. Additionally, the annealing ofdeposited dielectrics and etch damage, for example, oxide depositionsand silicon etches utilized in the transferred layer isolationprocessing, for example, STI (Shallow Trench Isolation) processing orstrained source and drain processing, may be accomplished by opticalannealing. Second device layer metal interconnect 461 may includeelectrically conductive materials such as copper, aluminum, conductiveforms of carbon, and tungsten. Donor wafer device structures 450 mayutilize second device layer metal interconnect 461 and thru layer vias(TLVs) 460 to electrically couple (connection paths) the donor waferdevice structures 450 to the acceptor wafer metal connect pads or strips480, and thus couple donor wafer device structures (the second layertransistors) with acceptor wafer device structures (first layertransistors). Thermal TLVs 462 may be constructed of thermallyconductive but not electrically conductive materials, for example, DLC(Diamond Like Carbon), and may connect donor wafer device structures 450thermally to shield/heat sink layer 488. TLVs 460 may be constructed outof electrically and thermally conductive materials, such as Tungsten,Copper, or aluminum, and may provide a thermal and electrical connectionpath from donor wafer device structures 450 to shield/heat sink layer488, which may be a ground or Vdd plane in the design/layout. TLVs 460and thermal TLVs 462 may be also constructed in the device scribelanes(pre-designed in base layers or potential dicelines) to provide thermalconduction to the heat sink, and may be sawed/diced off when the waferis diced for packaging. Shield/heat sink layer 488 may be configured toact as an emf (electro-motive force) shield to prevent direct layer tolayer cross-talk between transistors in the donor wafer layer andtransistors in the acceptor wafer. In addition to static ground or Vddbiasing, shield/heat sink layer 488 may be actively biased with ananti-interference signal from circuitry residing on, for example, alayer of the 3D-IC or off chip. TLVs 460 may be formed through thetransferred layers 402. As the transferred layers 402 may be thin, onthe order of about 200 nm or less in thickness, the TLVs may be easilymanufactured as a typical metal to metal via may be, and said TLV mayhave state of the art diameters such as nanometers or tens to a fewhundreds of nanometers, such as, for example about 150 nm or about 100nm or about 50 nm. The thinner the transferred layers 402, the smallerthe thru layer via diameter obtainable, which may result frommaintaining manufacturable via aspect ratios. Thus, the transferredlayers 402 (and hence, TLVs 460) may be, for example, less than about 2microns thick, less than about 1 micron thick, less than about 0.4microns thick, less than about 200 nm thick, less than about 150 nmthick, less than about 100 nm thick, less than about 50 nm thick, lessthan about 20 nm thick, or less than about 5 nm thick. The thickness ofthe layer or layers transferred according to some embodiments of theinvention may be designed as such to match and enable the most suitableobtainable lithographic resolution (and enable the use of conventionalstate of the art lithographic tools), such as, for example, less thanabout 10 nm, 14 nm, 22 nm or 28 nm linewidth resolution and alignmentcapability, such as, for example, less than about 5 nm, 10 nm, 20 nm, or40 nm alignment accuracy/precision/error, of the manufacturing processemployed to create the thru layer vias or any other structures on thetransferred layer or layers. The above TLV dimensions and alignmentcapability and transferred layer thicknesses may be also applied to anyof the discussed TLVs or transferred layers described elsewhere herein.Transferred layers 402 may be considered to be overlying the metal layeror layers of acceptor wafer 410. Alignment marks in acceptor wafer 410and/or in transferred layers 402 may be utilized to enable reliablecontact to transistors and circuitry in transferred layers 402 and donorwafer device structures 450 and electrically couple them to thetransistors and circuitry in the acceptor wafer 410. The donor wafer 400may now also be processed, such as smoothing and annealing, and reusedfor additional layer transfers. The transferred layers 402 and otheradditional regions created in the transferred layers during transistorprocessing are thin and small, having small volumes on the order of2×10⁻¹⁶ cm³ (2×10⁵ nm³ for a 100 nm by 100 nm×20 nm thick device). As aresult, the amount of energy to manufacture with known in the arttransistor and device formation processing, for example, annealing ofion-cut created defects or activation of dopants and annealing of dopingor etching damages, is very small and may lead to only a small amount ofshield layer or layers or regions or none to effectively shield theunderlying interconnect metallization and dielectrics from themanufacturing processing generated heat. The energy may be supplied by,for example, pulsed and short wavelength optical annealing techniquesdescribed herein and incorporated references, and may include the use ofoptical absorbers and reflectors and optical/thermal shielding and heatspreaders, some of which are described herein and incorporatedreferences.

As illustrated in FIG. 4F, a thermal conduction path may be constructedfrom the devices in the upper layer, the transferred donor layer andformed transistors, to the acceptor wafer substrate and associated heatsink. The thermal conduction path from the donor wafer device structures450 to the acceptor wafer heat sink 497 may include second device layermetal interconnect 461, TLVs 460, shield path connect 485, shield pathvia 483, metal connect pads or strips 480, first (acceptor) layer metalinterconnect 491, acceptor wafer transistors and devices 493, andacceptor substrate 495. The elements of the thermal conduction path mayinclude materials that have a thermal conductivity greater than 10W/m-K, for example, copper (about 400 W/m-K), aluminum (about 237W/m-K), and Tungsten (about 173 W/m-K), and may include material withthermal conductivity lower than 10 W/m-K but have a high heat transfercapacity due to the wide area available for heat transfer and thicknessof the structure (Fourier's Law), such as, for example, acceptorsubstrate 495. The elements of the thermal conduction path may includematerials that are thermally conductive but may not be substantiallyelectrically conductive, for example, Plasma Enhanced Chemical VaporDeposited Diamond Like Carbon-PECVD DLC (about 1000 W/m-K), and ChemicalVapor Deposited (CVD) graphene (about 5000 W/m-K). The acceptor waferinterconnects may be substantially surrounded by BEOL dielectric 496. Ingeneral, within the active device or devices (that are generating theheat that is desired to be conducted away thru at least the thermalconduction path), it would be advantageous to have an effectiveconduction path to reduce the overall space and area that a designerwould allocate for heat transfer out of the active circuitry space andarea. A designer may select to use only materials with a high thermalconductivity (such as greater than 10 W/m-K), much higher for examplethan that for monocrystalline silicon, for the desired thermalconduction path. However, there may need to be lower than desiredthermal conductivity materials in the heat conduction path due torequirements such as, for example, the mechanical strength of a thicksilicon substrate, or another heat spreader material in the stack. Thearea and volume allocated to that structure, such as the siliconsubstrate, is far larger than the active circuit area and volume.Accordingly, since a copper wire of 1 um³ profile is about the same as a286 um³ profile of a column of silicon, and the thermal conduction pathmay include both a copper wire/TLV/via and the bulk silicon substrate, aproper design may take into account and strive to align the differentelements of the conductive path to achieve effective heat transfer andremoval, for example, may attempt to provide about 286 times the siliconsubstrate area for each Cu thermal via utilized in the thermalconduction path. The heat removal apparatus, which may include acceptorwafer heat sink 497, may include an external surface from which heattransfer may take place by methods such as air cooling, liquid cooling,or attachment to another heat sink or heat spreader structure.

Formation of CMOS in one transferred layer and the orthogonal connectstrip methodology may be found as illustrated in at least FIGS. 30-33,73-80, and 94 and related specification sections of U.S. Pat. No.8,273,610, and may be applied to at least the FIG. 4 formationtechniques.

A planar fully depleted n-channel MOSFET (FD-MOSFET) with an optionalintegrated heat shield/spreader suitable for a monolithic 3D IC may beconstructed as follows. The FD-MOSFET may provide an improved transistorvariability control and conduction channel electrostatic control, aswell as the ability to utilize an updoped channel, thereby improvingcarrier mobility. In addition, the FD-MOSFET does not demand doping orpocket implants in the channel to control the electrostaticcharacteristics and tune the threshold voltages. Sub-threshold slope,DIBL, and other short channel effects are greatly improved due to thefirm gate electrostatic control over the channel. Moreover, a heatspreading, heat conducting and/or optically reflecting material layer orlayers may be incorporated between the sensitive metal interconnectlayers and the layer or regions being optically irradiated and annealedto repair defects in the crystalline 3D-IC layers and regions and toactivate semiconductor dopants in the crystalline layers or regions of a3D-IC without harm to the sensitive metal interconnect and associateddielectrics. FIG. 5A-5H illustrates an exemplary re-channel FD-MOSFETwhich may be constructed in a 3D stacked layer using procedures outlinedbelow and in U.S. Pat. Nos. 8,273,610 and 8,557,632 and 8,581,349. Thecontents of the foregoing applications are incorporated herein byreference.

As illustrated in FIG. 5A, a P-substrate donor wafer 500 may beprocessed to include a wafer sized layer of doping across the wafer. Thechannel layer 502 may be formed by ion implantation and thermal anneal.P-substrate donor wafer 500 may include a crystalline material, forexample, mono-crystalline (single crystal) silicon. P-substrate donorwafer 500 may be very lightly doped (less than 1e15 atoms/cm³) ornominally un-doped (less than 1e14 atoms/cm³). Channel layer 502 mayhave additional ion implantation and anneal processing to provide adifferent dopant level than P-substrate donor wafer 500 and may havegraded or various layers of doping concentration. The layer stack mayalternatively be formed by epitaxially deposited doped or undopedsilicon layers, or by a combination of epitaxy and implantation, or bylayer transfer. Annealing of implants and doping may include, forexample, conductive/inductive thermal, optical annealing techniques ortypes of Rapid Thermal Anneal (RTA or spike). The preferred crystallinechannel layer 502 will be undoped to eventually create an FD-MOSFETtransistor with an updoped conduction channel.

As illustrated in FIG. 5B, the top surface of the P-substrate donorwafer 500 layer stack may be prepared for oxide wafer bonding with adeposition of an oxide or by thermal oxidation of channel layer 502 toform oxide layer 580. A layer transfer demarcation plane (shown asdashed line) 599 may be formed by hydrogen implantation or other methodsas described in the incorporated references. The P-substrate donor wafer500, such as surface 582, and acceptor wafer 510 may be prepared forwafer bonding as previously described and low temperature (less thanapproximately 400° C.) bonded. Acceptor wafer 510, as described in theincorporated references, may include, for example, transistors,circuitry, and metal, such as, for example, aluminum or copper,interconnect wiring, a metal shield/heat sink layer or layers, and thrulayer via metal interconnect strips or pads. Acceptor wafer 510 may besubstantially comprised of a crystalline material, for examplemono-crystalline silicon or germanium, or may be an engineeredsubstrate/wafer such as, for example, an SOI (Silicon on Insulator)wafer or GeOI (Germanium on Insulator) substrate. Acceptor wafer 510 mayinclude transistors such as, for example, MOSFETS, FD-MOSFETS, FinFets,FD-RCATs, BJTs, HEMTs, and/or HBTs. The portion of the channel layer 502and the P-substrate donor wafer 500 that may be above (when the layerstack is flipped over and bonded to the acceptor wafer 510) the layertransfer demarcation plane 599 may be removed by cleaving or other lowtemperature processes as described in the incorporated references, suchas, for example, ion-cut with mechanical or thermal cleave or otherlayer transfer methods, thus forming remaining channel layer 503.Damage/defects to crystalline structure of channel layer 502 may beannealed by some of the annealing methods described, for example theshort wavelength pulsed laser techniques, wherein the channel layer 502or portions of channel layer 502 may be heated to defect annealingtemperatures, but the layer transfer demarcation plane 599 may be keptbelow the temperate for cleaving and/or significant hydrogen diffusion.The optical energy may be deposited in the upper layer of the stack, forexample near surface 582, and annealing of a portion of channel layer502 may take place via heat diffusion.

As illustrated in FIG. 5C, oxide layer 580 and remaining channel layer503 have been layer transferred to acceptor wafer 510. The top surfaceof remaining channel layer 503 may be chemically or mechanicallypolished, and/or may be thinned by low temperature oxidation and stripprocesses, such as the TEL SPA tool radical oxidation and HF:H₂Osolutions as described herein and in referenced patents and patentapplications. Thru the processing, the wafer sized layer remainingchannel layer 503 could be thinned from its original total thickness,and its final total thickness could be in the range of about 5 nm toabout 20 nm, for example, 5 nm, 7 nm, 10 nm, 12 nm, 15 nm, or 20 nm.Remaining channel layer 503 may have a thickness and doping that mayallow fully-depleted channel operation when the FD-MOSFET transistor issubstantially completely formed. Acceptor wafer 510 may include one ormore (two are shown in this example) shield/heat sink layers 588, whichmay include materials such as, for example, Aluminum, Tungsten (arefractory metal), Copper, silicon or cobalt based silicides, or formsof carbon such as carbon nanotubes. Each shield/heat sink layer 588 mayhave a thickness range of about 50 nm to about 1 mm, for example, 50 nm,100 nm, 200 nm, 300 nm, 500 nm, 0.1 um, 1 um, 2 um, and 10 um.Shield/heat sink layer 588 may include isolation openings 587, andalignment mark openings (not shown), which may be utilized for shortwavelength alignment of top layer (donor) processing to the acceptorwafer alignment marks (not shown). Shield/heat sink layer 588 mayinclude one or more shield path connects 585 and shield path vias 583.Shield path via 583 may thermally and/or electrically couple and connectshield path connect 585 to acceptor wafer 510 interconnect metallizationlayers such as, for example, exemplary acceptor metal interconnect 581(shown). Shield path connect 585 may also thermally and/or electricallycouple and connect each shield/heat sink layer 588 to the other and toacceptor wafer 510 interconnect metallization layers such as, forexample, acceptor metal interconnect 581, thereby creating a heatconduction path from the shield/heat sink layer 588 to the acceptorsubstrate 595, and a heat sink (shown in FIG. 5G). Isolation openings587 may include dielectric materials, similar to those of BEOL isolation596. Acceptor wafer 510 may include first (acceptor) layer metalinterconnect 591, acceptor wafer transistors and devices 593, andacceptor substrate 595. Various topside defect anneals may be utilized.For this illustration, an optical beam such as the laser annealingpreviously described is used. Optical anneal beams may be optimized tofocus light absorption and heat generation within or at the surface ofremaining channel layer 503 and provide surface smoothing and/or defectannealing (defects may be from the cleave and/or the ion-cutimplantation) with exemplary smoothing/annealing ray 566. The laserassisted smoothing/annealing with the absorbed heat generated byexemplary smoothing/annealing ray 566 may also include a pre-heat of thebonded stack to, for example, about 100° C. to about 400° C., and/or arapid thermal spike to temperatures above about 200° C. to about 600° C.Additionally, absorber layers or regions, for example, includingamorphous carbon, amorphous silicon, and phase changing materials (seeU.S. Pat. Nos. 6,635,588 and 6,479,821 to Hawryluk et al. for example),may be utilized to increase the efficiency of the optical energy capturein conversion to heat for the desired annealing or activation processes.Moreover, multiple pulses of the laser may be utilized to improve theanneal, activation, and yield of the process. Reflected ray 563 may bereflected and/or absorbed by shield/heat sink layer 588 regions thusblocking the optical absorption of ray blocked metal interconnect 581.Annealing of dopants or annealing of damage, such as from the H cleaveimplant damage, may be also accomplished by a set of rays such as repairray 565. Heat generated by absorbed photons from, for example,smoothing/annealing ray 566, reflected ray 563, and/or repair ray 565may also be absorbed by shield/heat sink layer 588 regions anddissipated laterally and may keep the temperature of underlying metallayers, such as metal interconnect 581, and other metal layers below it,cooler and prevent damage. Shield/heat sink layer 588 and associateddielectrics may laterally spread and conduct the heat generated by thetopside defect anneal, and in conjunction with the dielectric materials(low heat conductivity) above and below shield/heat sink layer 588, keepthe interconnect metals and low-k dielectrics of the acceptor waferinterconnect layers cooler than a damage temperature, such as, forexample, 400° C. A second layer of shield/heat sink layer 588 may beconstructed (shown) with a low heat conductive material sandwichedbetween the two heat sink layers, such as silicon oxide or carbon dopedlow-k′ silicon oxides, for improved thermal protection of the acceptorwafer interconnect layers, metal and dielectrics. Shield/heat sink layer588 may act as a heat spreader. Electrically conductive materials may beused for the two layers of shield/heat sink layer 588 and thus mayprovide, for example, a Vss and a Vdd plane that may be connected to thedonor layer transistors above, as well may be connected to the acceptorwafer transistors below, and/or may provide below transferred layerdevice interconnection. Shield/heat sink layer 588 may include materialswith a high thermal conductivity greater than 10 W/m-K, for example,copper (about 400 W/m-K), aluminum (about 237 W/m-K), Tungsten (about173 W/m-K), Plasma. Enhanced Chemical Vapor Deposited Diamond LikeCarbon-PECVD DLC (about 1000 W/m-K), and Chemical Vapor Deposited (CVD)graphene (about 5000 W/m-K). Shield/heat sink layer 588 may besandwiched and/or substantially enclosed by materials with a low thermalconductivity (less than 10 W/m-K), for example, silicon dioxide (about1.4 W/m-K). The sandwiching of high and low thermal conductivitymaterials in layers, such as shield/heat sink layer 588 and under &overlying dielectric layers, spreads the localized heat/light energy ofthe topside anneal laterally and protects the underlying layers ofinterconnect metallization & dielectrics, such as in the acceptor wafer510, from harmful temperatures or damage. When there may be more thanone shield/heat sink layer 588 in the device, the heat conducting layerclosest to the second crystalline layer or oxide layer 580 may beconstructed with a different material, for example a high melting pointmaterial, for example a refractory metal such as tungsten, than theother heat conducting layer or layers, which may be constructed with,for example, a lower melting point material, for example, such asaluminum or copper. Now transistors may be formed with low effectivetemperature (less than approximately 400° C. exposure to the acceptorwafer 510 sensitive layers, such as interconnect and device layers)processing, and may be aligned to the acceptor wafer alignment marks(not shown) as described in the incorporated references. This mayinclude further optical defect annealing or dopant activation steps. Thedonor wafer 500 may now also be processed, such as smoothing andannealing, and reused for additional layer transfers. The insulatorlayer, such as deposited bonding oxides (for example oxide layer 580)and/or before bonding preparation existing oxides (for example the BEOLisolation 596 on top of the topmost metal layer of shield/heat sinklayer 588), between the donor wafer transferred monocrystalline layerand the acceptor wafer topmost metal layer, may include thicknesses ofless than 1 um, less than 500 nm, less than 400 nm, less than 300 nm,less than 200 nm, or less than 100 nm.

As illustrated in FIG. 5D, transistor isolation regions 505 may beformed by mask defining and plasma/RIE etching remaining channel layer503 substantially to the top of oxide layer 580 (not shown),substantially into oxide layer 580, or into a portion of the upper oxidelayer of acceptor wafer 510 (not shown). Thus channel region 523 may beformed, which may substantially form the transistor body. Alow-temperature gap fill dielectric, such as SACVD oxide, may bedeposited and chemically mechanically polished, the oxide remaining inisolation regions 505. An optical step, such as illustrated by exemplarySTI ray 567, may be performed to anneal etch damage and densify the STIoxide in isolation regions 505. The doping concentration of the channelregion 523 may include gradients of concentration or layers of differingdoping concentrations. Any additional doping, such as ion-implantedchannel implants, may be activated and annealed with optical annealing,such as illustrated by exemplary implant ray 569, as described herein.The optical anneal, such as exemplary STI ray 567, and/or exemplaryimplant ray 569 may be performed at separate times and processingparameters (such as laser energy, frequency, etc.) or may be done incombination or as one optical anneal. Optical absorber and or reflectivelayers or regions may be employed to enhance the anneal and/or protectthe underlying sensitive structures. Moreover, multiple pulses of thelaser may be utilized to improve the anneal, activation, and yield ofthe process.

As illustrated in FIG. 5E, a transistor forming process, such as aconventional HKMG with raised source and drains (S/D), may be performed.For example, a dummy gate stack (not shown), utilizing oxide andpolysilicon, may be formed, gate spacers 530 may be formed, raised S/Dregions 532 and channel stressors may be formed by etch and epitaxialdeposition, for example, of SiGe and/or SiC depending on P or N channel,LDD and S/D ion-implantations may be performed, and first ILD 536 may bedeposited and CMP′d to expose the tops of the dummy gates. Thustransistor channel 533 and S/D & LDD regions 535 may be formed. Thedummy gate stack may be removed and a gate dielectric 507 may be formedand a gate metal material gate electrode 508, including a layer ofproper work function metal (Ti_(x)Al_(y)N_(z) for example) and aconductive fill, such as aluminum, and may be deposited and CMP′d. Thegate dielectric 507 may be an atomic layer deposited (ALD) gatedielectric that may be paired with a work function specific gate metalin the industry standard high k metal gate process schemes, for example,as described in the incorporated references. Alternatively, the gatedielectric 507 may be formed with a low temperature processes including,for example, LPCVD SiO₂ oxide deposition (see Ahn, J., et al.,“High-quality MOSFET's with ultrathin LPCVD gate SiO2,” IEEE ElectronDevice Lett., vol. 13, no. 4, pp. 186-188, April 1992) or lowtemperature microwave plasma oxidation of the silicon surfaces (see Kim,J. Y., et al., “The excellent scalability of the RCAT(recess-channel-array-transistor) technology for sub-70 nm DRAM featuresize and beyond,” 2005 IEEE VLSI-TSA International Symposium, pp. 4-5,25-27 Apr. 2005) and a gate material with proper work function and lessthan approximately 400° C. deposition temperature such as, for example,tungsten or aluminum may be deposited. An optical step, such asrepresented by exemplary anneal ray 521, may be performed to densifyand/or remove defects from gate dielectric 507, anneal defects andactivate dopants such as LDD and S/D implants, densify the first ILD536, and/or form contact and S/D silicides (not shown). The opticalanneal may be performed at each sub-step as desired, or may be done atprior to the HKMG deposition, or various combinations. Moreover,multiple pulses of the laser may be utilized to improve the anneal,activation, and yield of the process.

As illustrated in FIG. 5F, a low temperature thick oxide 509 may bedeposited and planarized Source, gate, and drain contacts openings maybe masked and etched preparing the transistors to be connected viametallization Thus gate contact 511 connects to gate electrode 508, andsource & drain contacts 540 connect to raised S/D regions 532. Anoptical step, such as illustrated by exemplary ILD anneal ray 551, maybe performed to anneal contact etch damage and densify the thick oxide509.

As illustrated in FIG. 5G, thru layer vias (TLVs) 560 may be formed byetching thick oxide 509, first ILD 536, isolation regions 505, oxidelayer 580, into a portion of the upper oxide layer BEOL isolation 596 ofacceptor wafer 510 BEOL, and filling with an electrically and thermallyconducting material (such as tungsten or cooper) or an electricallynon-conducting but thermally conducting material (such as describedelsewhere within). Second device layer metal interconnect 561 may beformed by conventional processing. TLVs 560 may be constructed ofthermally conductive but not electrically conductive materials, forexample, DLC (Diamond Like Carbon), and may connect the FD-MOSFETtransistor device and other devices on the top (second) crystallinelayer thermally to shield/heat sink layer 588. TLVs 560 may beconstructed out of electrically and thermally conductive materials, suchas Tungsten, Copper, or aluminum, and may provide a thermal andelectrical connection path from the FD-MOSFET transistor device andother devices on the top (second) crystalline layer to shield/heat sinklayer 588, which may be a ground or Vdd plane in the design/layout. TLVs560 may be also constructed in the device scribelanes (pre-designed inbase layers or potential dicelines) to provide thermal conduction to theheat sink, and may be sawed/diced off when the wafer is diced forpackaging not shown). Shield/heat sink layer 588 may be configured toact (or adapted to act) as an emf (electro-motive force) shield toprevent direct layer to layer cross-talk between transistors in thedonor wafer layer and transistors in the acceptor wafer. In addition tostatic ground or Vdd biasing, shield/heat sink layer 588 may be activelybiased with an anti-interference signal from circuitry residing on, forexample, a layer of the 3D-IC or off chip. The formed FD-MOSFETtransistor device may include semiconductor regions wherein the dopantconcentration of neighboring regions of the transistor in the horizontalplane, such as traversed by exemplary dopant plane 534, may haveregions, for example, transistor channel 533 and S/D & LDD regions 535,that differ substantially in dopant concentration, for example, a 10times greater doping concentration in S/D & LDD regions 535 than intransistor channel 533, and/or may have a different dopant type, suchas, for example p-type or n-type dopant, and/or may be doped andsubstantially undoped in the neighboring regions. For example,transistor channel 533 may be very lightly doped (less than 1e15atoms/cm³) or nominally un-doped (less than 1e14 atoms/cm³) and S/D &LDD regions 535 may be doped at greater than 1e15 atoms/cm³ or greaterthan 1e16 atoms/cm³. For example, transistor channel 533 may be dopedwith p-type dopant and S/D & LDD regions 535 may be doped with n-typedopant.

A thermal conduction path may be constructed from the devices in theupper layer, the transferred donor layer and formed transistors, to theacceptor wafer substrate and associated heat sink. The thermalconduction path from the FD-MOSFET transistor device and other deviceson the top (second) crystalline layer, for example, raised S/D regions532, to the acceptor wafer heat sink 597 may include source & draincontacts 540, second device layer metal interconnect 561, TLV 560,shield path connect 585 (shown as twice), shield path via 583 (shown astwice), metal interconnect 581, first (acceptor) layer metalinterconnect 591, acceptor wafer transistors and devices 593, andacceptor substrate 595. The elements of the thermal conduction path mayinclude materials that have a thermal conductivity greater than 10W/m-K, for example, copper (about 400 W/m-K), aluminum (about 237W/m-K), and Tungsten (about 173 W/m-K), and may include material withthermal conductivity lower than 10 W/m-K but have a high heat transfercapacity due to the wide area available for heat transfer and thicknessof the structure (Fourier's Law), such as, for example, acceptorsubstrate 595. The elements of the thermal conduction path may includematerials that are thermally conductive but may not be substantiallyelectrically conductive, for example, Plasma Enhanced Chemical VaporDeposited Diamond Like Carbon-PECVD DLC (about 1000 W/m-K), and ChemicalVapor Deposited (CVD) graphene (about 5000 W/m-K). The acceptor waferinterconnects may be substantially surrounded by BEOL isolation 596dielectric. The heat removal apparatus, which may include acceptor waferheat sink 597, may include an external surface from which heat transfermay take place by methods such as air cooling, liquid cooling, orattachment to another heat sink or heat spreader structure.

Furthermore, some or all of the layers utilized as shield/heat sinklayer 588, which may include shapes of material such as the strips orfingers as illustrated in FIG. 4G, may be driven by a portion of thesecond layer transistors and circuits (within the transferred donorwafer layer or layers) or the acceptor wafer transistors and circuits,to provide a programmable back-bias to at least a portion of the secondlayer transistors. The programmable back bias may utilize a circuit todo so, for example, such as shown in FIG. 17B of U.S. Pat. No.8,273,610, the contents incorporated herein by reference; wherein the‘Primary’ layer may be the second layer of transistors for which theback-bias is being provided, the ‘Foundation’ layer could be either thesecond layer transistors (donor) or first layer transistors (acceptor),and the routing metal lines connections 1723 and 1724 may includeportions of the shield/heat sink layer 588 layer or layers. Moreover,some or all of the layers utilized as shield/heat sink layer 588, whichmay include strips or fingers as illustrated in FIG. 4G, may be drivenby a portion of the second layer transistors and circuits (within thetransferred donor wafer layer or layers) or the acceptor wafertransistors and circuits to provide a programmable power supply to atleast a portion of the second layer transistors. The programmable powersupply may utilize a circuit to do so, for example, such as shown inFIG. 17C of U.S. Pat. No. 8,273,610, the contents incorporated herein byreference; wherein the ‘Primary’ layer may be the second layer oftransistors for which the programmable power supplies are being providedto, the ‘Foundation’ layer could be either the second layer transistors(donor) or first layer transistors (acceptor), and the routing metalline connections from Vout to the various second layer transistors mayinclude portions of the shield/heat sink layer 588 layer or layers. TheVsupply on line 17C12 and the control signals on control line 17C16 maybe controlled by and/or generated in the second layer transistors (forexample donor wafer device structures such as the FD-MOSFETs formed asdescribed in relation to FIG. 5) or first layer transistors (acceptor,for example acceptor wafer transistors and devices 593), or off chipcircuits. Furthermore, some or all of the layers utilized as shield/heatsink layer 588, which may include strips or fingers as illustrated inFIG. 4G or other shapes such as those in FIG. 4B, may be utilized todistribute independent power supplies to various portions of the secondlayer transistors (for example donor wafer device structures such as theFD-MOSFETs formed as described in relation to FIG. 5) or first layertransistors (acceptor, for example acceptor wafer transistors anddevices 593) and circuits; for example, one power supply and/or voltagemay be routed to the sequential logic circuits of the second layer and adifferent power supply and/or voltage routed to the combinatorial logiccircuits of the second layer. Patterning of shield/heat sink layer 588or layers can impact their heat-shielding capacity. This impact may bemitigated, for example, by enhancing the top shield/heat sink layer 588areal density, creating more of the secondary shield/heat sink layers588, or attending to special CAD rules regarding their metal density,similar to CAD rules that are required to accommodateChemical-Mechanical Planarization (CMP). These constraints would beintegrated into a design and layout EDA tool.

TLVs 560 may be formed through the transferred layers. As thetransferred layers may be thin, on the order of about 200 nm or less inthickness, the TLVs may be easily manufactured as a typical metal tometal via may be, and said TLV may have state of the art diameters suchas nanometers or tens to a few hundreds of nanometers, such as, forexample about 150 nm or about 100 nm or about 50 nm. The thinner thetransferred layers, the smaller the thru layer via diameter obtainable,which may result from maintaining manufacturable via aspect ratios. Thethickness of the layer or layers transferred according to someembodiments of the invention may be designed as such to match and enablethe most suitable obtainable lithographic resolution (and enable the useof conventional state of the art lithographic tools), such as, forexample, less than about 10 nm, 14 nm, 22 nm or 28 nm linewidthresolution and alignment capability, such as, for example, less thanabout 5 nm, 10 nm, 20 nm, or 40 nm alignment accuracy/precision/error,of the manufacturing process employed to create the thru layer vias orany other structures on the transferred layer or layers.

As illustrated in FIG. 5H, at least one conductive bond pad 564 forinterfacing electrically (and may thermally) to external devices may beformed on top of the completed device and may include at least one metallayer of second device layer metal interconnect 561. Bond pad 564 mayoverlay second device layer metal interconnect 561 or a portion of (someof the metal and insulator layers of) second device layer metalinterconnect 561. Bond pad 564 may be directly aligned to the acceptorwafer alignment marks (not shown) and the I/O driver circuitry may beformed by the second layer (donor) transistors, for example, donor waferdevice structures such as the FD-MOSFETs formed as described in relationto FIG. 5. Bond pad 564 may be connected to the second layer transistorsthru the second device layer metal interconnect 561 which may includevias 562. The I/O driver circuitry may be formed by transistors from theacceptor wafer transistors and devices 593, or from transistors in otherstrata if the 3DIC device has more than two layers of transistors. I/Opad control metal segment 567 may be formed directly underneath bond pad564 and may influence the noise and ESD (Electro Static Discharge)characteristics of bond pad 564. The emf influence of I/O pad controlmetal segment 567 may be controlled by circuitry formed from a portionof the second layer transistors. I/O pad control metal segment 567 maybe formed with second device layer metal interconnect 561. Furthermore,metal segment 589 of the topmost shield/heat sink layer 588 may be usedto influence the FD-MOSFET transistor or transistors above it by emf,and influence the noise and ESD (Electro Static Discharge)characteristics of bond pad 564. Metal segment 589 may be controlled bysecond layer (donor) transistors, for example, donor wafer devicestructures such as the FD-MOSFETs formed as described in relation toFIG. 5 and/or by transistors from the acceptor wafer transistors anddevices 593, or from transistors in other strata if the 3DIC device hasmore than two layers of transistors.

Formation of CMOS in one transferred layer and the orthogonal connectstrip methodology may be found as illustrated in at least FIGS. 30-33,73-80, and 94 and related specification sections of U.S. Pat. No.8,273,610, and may be applied to at least the FIG. 5 formationtechniques herein.

Persons of ordinary skill in the art will appreciate that theillustrations in FIGS. 5A through 5H are exemplary only and are notdrawn to scale. Such skilled persons will further appreciate that manyvariations are possible such as, for example, a p-channel FD-MOSFET maybe formed with changing the types of dopings appropriately. Moreover,the P-substrate donor wafer 500 may be n type or un-doped. Furthermore,isolation regions 505 may be formed by a hard mask defined process flow,wherein a hard mask stack, such as, for example, silicon oxide andsilicon nitride layers, or silicon oxide and amorphous carbon layers,may be utilized. Moreover, CMOS FD MOSFET s may be constructed withn-MOSFETs in a first mono-crystalline silicon layer and p− MOSFET s in asecond mono-crystalline layer, which may include different crystallineorientations of the mono-crystalline silicon layers, such as forexample, <100>, <111> or <551>, and may include different contactsilicides for optimum contact resistance to p or n type source, drains,and gates. Further, dopant segregation techniques (DST) may be utilizedto efficiently modulate the source and drain Schottky barrier height forboth p and n type junctions formed. Furthermore, raised source and draincontact structures, such as etch and epi SiGe and SiC, may be utilizedfor strain and contact resistance improvements and the damage from theprocesses may be optically annealed. Many other modifications within thescope of the invention will suggest themselves to such skilled personsafter reading this specification. Thus the invention is to be limitedonly by the appended claims.

In many applications it is desired to use a combination of N typetransistors and P type transistors. While using two overlaid layers, atleast one layer of P type transistors on top of at least one layer of Ntype transistors, has been previously described herein and n referencedpatent applications, it might be desired to have those transistorsconnected by the same overlaying interconnection layers coupling to onetransistor layer. In U.S. Pat. No. 8,273,610, the contents of which areincorporated herein by reference, there are at least two flows toprovide such. The flows could be adapted to vertical transistors just aswell. The first flow suggests using repeating rows of N type and P typeand is detailed in at least FIGS. 20-35 and FIGS. 73-79 of U.S. Pat. No.8,273,610. An alternative flow suggests using layers within the stratain a vertical manner, and is described in at least FIG. 95 of U.S. Pat.No. 8,273,610.

While concepts in this document have been described with respect to3D-ICs with two stacked device layers, those of ordinary skill in theart will appreciate that it can be valid for 3D-ICs with more than twostacked device layers. Additionally, some of the concepts may be appliedto 2D ICs.

An additional embodiment of the invention is to utilize the underlyinginterconnection layer or layers to provide connections and connectionpaths (electrical and/or thermal) for the overlying transistors. Whilethe common practice in the IC industry is that interconnection layersare overlaying the transistors that they connect, the 3D IC technologymay include the possibility of constructing connections underneath(below) the transistors as well. For example, some of the connectionsto, from, and in-between transistors in a layer of transistors may beprovided by the interconnection layer or layers above the transistorlayer; and some of the connections to, from, and in-between thetransistors may be provided by the interconnection layer or layers belowthe transistor layer or layers. In general there is an advantage to havethe interconnect closer to the transistors that they are connecting andusing both sides of the transistors—both above and below—providesenhanced “closeness” to the transistors. In addition, there may be lessinterconnect routing congestion that would impede the efficient orpossible connection of a transistor to transistors in other layers andto other transistors in the same layer.

The connection layers may, for example, include power delivery, heatremoval, macro-cell connectivity, and routing between macro-cells.

One method to solve the issue of high-temperature source-drain junctionprocessing is to make transistors without junctions i.e. Junction-LessTransistors (JLTs). An embodiment of this invention uses JLTs as abuilding block for 3D stacked semiconductor circuits and chips.

FIG. 6 shows a schematic of a junction-less transistor (JLT) alsoreferred to as a gated resistor or nano-wire. A heavily doped siliconlayer (typically above 1×10¹⁹/cm³, but can be lower as well) formssource 0604, drain 0602 as well as channel region of a JLT. A gateelectrode 0606 and a gate dielectric 0608 are present over the channelregion of the JLT. The JLT has a very small channel area (typically lessthan 20 nm on one side), so the gate can deplete the channel of chargecarriers at 0V and turn it off. I-V curves of n channel (0612) and pchannel (0610) junction-less transistors are shown in FIG. 6 as well.These indicate that the JLT can show comparable performance to atri-gate transistor that is commonly researched by transistordevelopers. Further details of the JLT can be found in “Junctionlessmultigate field-effect transistor,” Appl. Phys. Lett., vol. 94, pp.053511 2009 by C.-W. Lee, A. Afzalian, N. Dehdashti Akhavan, R. Yan, I.Ferain and J. P. Colinge (“C-W. Lee”). Contents of this publication areincorporated herein by reference.

FIGS. 7A-M describe an alternative process flow to construct ahorizontally-oriented monolithic 3D DRAM. This monolithic 3D DRAMutilizes the floating body effect and double-gate transistors. One maskis utilized on a “per-memory-layer” basis for the monolithic 3D DRAMconcept shown in FIG. 7A-M, while other masks are shared betweendifferent layers. The process flow may include several steps that occurin the following sequence.

Step (A): Peripheral circuits 702 with tungsten wiring are firstconstructed and above this oxide layer 704 is deposited. FIG. 7Aillustrates the structure after Step (A).

Step (B): FIG. 7B shows a drawing illustration after Step (B). A p−Silicon wafer 706 has an oxide layer 708 grown or deposited above it.Following this, hydrogen is implanted into the p− Silicon wafer at acertain depth indicated by 710. Alternatively, some other atomic speciessuch as Helium could be (co-)implanted. This hydrogen implanted p−Silicon wafer 706 forms the top layer 712. The bottom layer 714 mayinclude the peripheral circuits 702 with oxide layer 704. The top layer712 is flipped and bonded to the bottom layer 714 using oxide-to-oxidebonding.Step (C): FIG. 7C illustrates the structure after Step (C). The stack oftop and bottom wafers after Step (B) is cleaved at the hydrogen plane710 using either a anneal or a sideways mechanical force or other means.A CMP process is then conducted. At the end of this step, asingle-crystal p− Si layer exists atop the peripheral circuits, and thishas been achieved using layer-transfer techniques.Step (D): FIG. 7D illustrates the structure after Step (D). Usinglithography and then implantation, n+ regions 716 and p-regions 718 areformed on the transferred layer of p− Si after Step (C).Step (E): FIG. 7E illustrates the structure after Step (E). An oxidelayer 720 is deposited atop the structure obtained after Step (D). Afirst layer of Si/SiO₂ 722 is therefore formed atop the peripheralcircuits 702.Step (F): FIG. 7F illustrates the structure after Step (F). Usingprocedures similar to Steps (B)-(E), additional Si/SiO₂ layers 724 and726 are formed atop Si/SiO₂ layer 722. A rapid thermal anneal (RTA) orspike anneal or flash anneal or laser anneal is then done to activateall implanted layers 722, 724 and 726 (and possibly also the peripheralcircuits 702). Alternatively, the layers 722, 724 and 726 are annealedlayer-by-layer as soon as their implantations are done using a laseranneal system.Step (G): FIG. 7G illustrates the structure after Step (G). Lithographyand etch processes are then utilized to make a structure as shown in thefigure.Step (H): FIG. 7H illustrates the structure after Step (H). Gatedielectric 728 and gate electrode 730 are then deposited following whicha CMP is done to planarize the gate electrode 730 regions. Lithographyand etch are utilized to define gate regions over the p− silicon regions(eg. p− Si region after Step (D)). Note that gate width could beslightly larger than p− region width to compensate for overlay errors inlithography.Step (I): FIG. 7I illustrates the structure after Step (I). A siliconoxide layer 732 is then deposited and planarized. For clarity, thesilicon oxide layer is shown transparent in the figure, along withword-line (WL) and source-line (SL) regions.Step (J): FIG. 7J illustrates the structure after Step (J). Bit-line(BL) contacts 734 are formed by etching and deposition. These BLcontacts are shared among all layers of memory.Step (K): FIG. 7K illustrates the structure after Step (K). BLs 736 arethen constructed. Contacts are made to BLs, WLs and SLs of the memoryarray at its edges. SL contacts can be made into stair-like structuresusing techniques described in “Bit Cost Scalable Technology with Punchand Plug Process for Ultra High Density Flash Memory,” VLSI Technology,2007 IEEE Symposium on, vol., no., pp. 14-15, 12-14 Jun. 2007 by Tanaka,H; Kido, M.; Yahashi, K.; Oomura, M.; et al., following which contactscan be constructed to them. Formation of stair-like structures for SLscould be done in steps prior to Step (K) as well.FIG. 7L shows cross-sectional views of the array for clarity. Thedouble-gated transistors in FIG. 7 L can be utilized along with thefloating body effect for storing information.FIG. 7M shows a memory cell of the floating body RAM array with twogates on either side of the p− Si layer 719.

A floating-body DRAM has thus been constructed, with (1)horizontally-oriented transistors—i.e., current flowing in substantiallythe horizontal direction in transistor channels, (2) some of the memorycell control lines, e.g., source-lines SL, constructed of heavily dopedsilicon and embedded in the memory cell layer, (3) side gatessimultaneously deposited over multiple memory layers, and (4)monocrystalline (or single-crystal) silicon layers obtained by layertransfer techniques such as ion-cut.

While many of today's memory technologies rely on charge storage,several companies are developing non-volatile memory technologies basedon resistance of a material changing. Examples of these resistance-basedmemories include phase change memory, Metal Oxide memory, resistive RAM(RRAM), memristors, solid-electrolyte memory, ferroelectric RAM,conductive bridge RAM, and MRAM. Background information on theseresistive-memory types is given in “Overview of candidate devicetechnologies for storage-class memory,” IBM Journal of Research andDevelopment, vol. 52, no. 4.5, pp. 449-464, July 2008 by Burr, G. W.;Kurdi, B. N.; Scott, J. C.; Lam, C. H.; Gopalakrishnan, K.; Shenoy, R.S.

FIG. 8A-J describe a novel memory architecture for resistance-basedmemories, and a procedure for its construction. The memory architectureutilizes junction-less transistors and has a resistance-based memoryelement in series with a transistor selector. No mask is utilized on a“per-memory-layer” basis for the monolithic 3D resistance change memory(or resistive memory) concept shown in FIG. 8A-J, and all other masksare shared between different layers. The process flow may includeseveral steps that occur in the following sequence.

Step (A): Peripheral circuits 802 are first constructed and above thisoxide layer 804 is deposited. FIG. 8A shows a drawing illustration afterStep (A).

Step (B): FIG. 8B illustrates the structure after Step (B). N+ Siliconwafer 808 has an oxide layer 806 grown or deposited above it. Followingthis, hydrogen is implanted into the n+ Silicon wafer at a certain depthindicated by 814. Alternatively, some other atomic species such asHelium could be (co-)implanted. This hydrogen implanted n+ Silicon wafer808 forms the top layer 810. The bottom layer 812 may include theperipheral circuits 802 with oxide layer 804. The top layer 810 isflipped and bonded to the bottom layer 812 using oxide-to-oxide bonding.Step (C): FIG. 8C illustrates the structure after Step (C). The stack oftop and bottom wafers after Step (B) is cleaved at the hydrogen plane814 using either a anneal or a sideways mechanical force or other means.A CMP process is then conducted. A layer of silicon oxide 818 is thendeposited atop the n+ Silicon layer 816. At the end of this step, asingle-crystal n+ Si layer 816 exists atop the peripheral circuits, andthis has been achieved using layer-transfer techniques.Step (D): FIG. 8D illustrates the structure after Step (D). Usingmethods similar to Step (B) and (C), multiple n+ silicon layers 820 areformed with silicon oxide layers in between.Step (E): FIG. 8E illustrates the structure after Step (E). Lithographyand etch processes are then utilized to make a structure as shown in thefigure.Step (F): FIG. 8F illustrates the structure after Step (F). Gatedielectric 826 and gate electrode 824 are then deposited following whicha CMP is performed to planarize the gate electrode 824 regions.Lithography and etch are utilized to define gate regions.Step (G): FIG. 8G illustrates the structure after Step (G). A siliconoxide layer 830 is then deposited and planarized. The silicon oxidelayer is shown transparent in the figure for clarity, along withword-line (WL) 832 and source-line (SL) 834 regions.Step (H): FIG. 8H illustrates the structure after Step (H). Vias areetched through multiple layers of silicon and silicon dioxide as shownin the figure. A resistance change memory material 836 is then deposited(preferably with atomic layer deposition (ALD)). Examples of such amaterial include hafnium oxide, well known to change resistance byapplying voltage. An electrode for the resistance change memory elementis then deposited (preferably using ALD) and is shown as electrode/BLcontact 840. A CMP process is then conducted to planarize the surface.It can be observed that multiple resistance change memory elements inseries with junction-less transistors are created after this step.Step (I): FIG. 8I illustrates the structure after Step (I). BLs 838 arethen constructed. Contacts are made to BLs, WLs and SLs of the memoryarray at its edges. SL contacts can be made into stair-like structuresusing techniques described in in “Bit Cost Scalable Technology withPunch and Plug Process for Ultra High Density Flash Memory,” VLSITechnology, 2007 IEEE Symposium on, vol., no., pp. 14-15, 12-14 Jun.2007 by Tanaka, H; Kido, M.; Yahashi, K.; Oomura, M.; et al., followingwhich contacts can be constructed to them. Formation of stair-likestructures for SLs could be achieved in steps prior to Step (I) as well.FIG. 8J shows cross-sectional views of the array for clarity.A 3D resistance change memory has thus been constructed, with (1)horizontally-oriented transistors—i.e. current flowing in substantiallythe horizontal direction in transistor channels, (2) some of the memorycell control lines, e.g., source-lines SL, constructed of heavily dopedsilicon and embedded in the memory cell layer, (3) side gates that aresimultaneously deposited over multiple memory layers for transistors,and (4) monocrystalline (or single-crystal) silicon layers obtained bylayer transfer techniques such as ion-cut.

While resistive memories described previously form a class ofnon-volatile memory, others classes of non-volatile memory exist. NANDflash memory forms one of the most common non-volatile memory types. Itcan be constructed of two main types of devices: floating-gate deviceswhere charge is stored in a floating gate and charge-trap devices wherecharge is stored in a charge-trap layer such as Silicon Nitride.Background information on charge-trap memory can be found in “IntegratedInterconnect Technologies for 3D Nanoelectronic Systems”, Artech House,2009 by Bakir and Meindl (“Bakir”) and “A Highly Scalable 8-Layer 3DVertical-Gate (VG) TFT NAND Flash Using Junction-Free Buried ChannelBE-SONOS Device,” Symposium on VLSI Technology, 2010 by Hang-Ting Lue,et al. The architectures shown in FIG. 9A-G are relevant for any type ofcharge-trap memory.

FIG. 9A-G describes a memory architecture for single-crystal 3Dcharge-trap memories, and a procedure for its construction. It utilizesjunction-less transistors. No mask is utilized on a “per-memory-layer”basis for the monolithic 3D charge-trap memory concept shown in FIG.9A-G, and all other masks are shared between different layers. Theprocess flow may include several steps as described in the followingsequence.

Step (A): Peripheral circuits 902 are first constructed and above thisoxide layer 904 is deposited. FIG. 9A shows a drawing illustration afterStep (A).

Step (B): FIG. 9B illustrates the structure after Step (B). A wafer ofn+ Silicon 908 has an oxide layer 906 grown or deposited above it.Following this, hydrogen is implanted into the n+ Silicon wafer at acertain depth indicated by 914. Alternatively, some other atomic speciessuch as Helium could be implanted. This hydrogen implanted n+ Siliconwafer 908 forms the top layer 910. The bottom layer 912 may include theperipheral circuits 902 with oxide layer 904. The top layer 910 isflipped and bonded to the bottom layer 912 using oxide-to-oxide bonding.Alternatively, n+ silicon wafer 908 may be doped differently, such as,for example, with elemental species that form a p+, or p−, or n− siliconwafer, or substantially absent of semiconductor dopants to form anundoped silicon wafer.Step (C): FIG. 9C illustrates the structure after Step (C). The stack oftop and bottom wafers after Step (B) is cleaved at the hydrogen plane914 using either a anneal or a sideways mechanical force or other means.A CMP process is then conducted. A layer of silicon oxide 918 is thendeposited atop the n+ Silicon layer 916. At the end of this step, asingle-crystal n+ Si layer 916 exists atop the peripheral circuits, andthis has been achieved using layer-transfer techniques.Step (D): FIG. 9D illustrates the structure after Step (D). Usingmethods similar to Step (B) and (C), multiple n+ silicon layers 920 areformed with silicon oxide layers in between.Step (E): FIG. 9E illustrates the structure after Step (E). Lithographyand etch processes are then utilized to make a structure as shown in thefigure.Step (F): FIG. 9F illustrates the structure after Step (F). Gatedielectric 926 and gate electrode 924 are then deposited following whicha CMP is done to planarize the gate electrode 924 regions. Lithographyand etch are utilized to define gate regions. Gates of the NAND string936 as well gates of select gates of the NAND string 938 are defined.Step (G): FIG. 9G illustrates the structure after Step (G). A siliconoxide layer 930 is then deposited and planarized. It is showntransparent in the figure for clarity. Word-lines, bit-lines andsource-lines are defined as shown in the figure. Contacts are formed tovarious regions/wires at the edges of the array as well. SL contacts canbe made into stair-like structures using techniques described in “BitCost Scalable Technology with Punch and Plug Process for Ultra HighDensity Flash Memory,” VLSI Technology, 2007 IEEE Symposium on, vol.,no., pp. 14-15, 12-14 Jun. 2007 by Tanaka, H.; Kido, M.; Yahashi, K.;Oomura, M.; et al., following which contacts can be constructed to them.Formation of stair-like structures for SLs could be performed in stepsprior to Step (G) as well.

A 3D charge-trap memory has thus been constructed, with (1)horizontally-oriented transistors—i.e. current flowing in substantiallythe horizontal direction in transistor channels, (2) some of the memorycell control lines—e.g., bit lines BL, constructed of heavily dopedsilicon and embedded in the memory cell layer, (3) side gatessimultaneously deposited over multiple memory layers for transistors,and (4) monocrystalline (or single-crystal) silicon layers obtained bylayer transfer techniques such as ion-cut. This use of single-crystalsilicon obtained with ion-cut is a key differentiator from past work on3D charge-trap memories such as “A Highly Scalable 8-Layer 3DVertical-Gate (VG) TFT NAND Flash Using Junction-Free Buried ChannelBE-SONOS Device,” Symposium on VLSI Technology, 2010 by Hang-Ting Lue,et al. that used polysilicon.

While the 3D DRAM and 3D resistive memory implementations herein havebeen described with single crystal silicon constructed with ion-cuttechnology, other options exist. One could construct them with selectiveepi technology. Procedures for doing these will be clear to thoseskilled in the art.

FIG. 10A-B show it is not the only option for the architecture, asdepicted in, for example, FIG. 28-FIG. 40A-H, and FIGS. 70-71 of U.S.Pat. No. 8,476,145, to have the peripheral transistors below the memorylayers. Peripheral transistors could also be constructed above thememory layers, as shown in FIG. 10B. This periphery layer would utilizetechnologies described herein, and could utilize transistors including,such as, junction-less transistors or recessed channel transistors.

The monolithic 3D integration concepts described in this patentapplication can lead to novel embodiments of poly-silicon-based memoryarchitectures as well. Poly silicon based architectures couldpotentially be cheaper than single crystal silicon based architectureswhen a large number of memory layers need to be constructed. While thebelow concepts are explained by using resistive memory architectures asan example, it will be clear to one skilled in the art that similarconcepts can be applied to NAND flash memory and DRAM architecturesdescribed previously in this patent application.

FIG. 11A-E shows one embodiment of the current invention, wherepolysilicon junction-less transistors are used to form a 3Dresistance-based memory. The utilized junction-less transistors can haveeither positive or negative threshold voltages. The process may includethe following steps as described in the following sequence:

Step (A): As illustrated in FIG. 11A, peripheral circuits 1102 areconstructed above which oxide layer 1104 is made.

Step (B): As illustrated in FIG. 11B, multiple layers of n+ dopedamorphous silicon or polysilicon 1106 are deposited with layers ofsilicon dioxide 1108 in between. The amorphous silicon or polysiliconlayers 1106 could be deposited using a chemical vapor depositionprocess, such as Low Pressure Chemical Vapor Deposition (LPCVD) orPlasma Enhanced Chemical Vapor Deposition (PECVD).Step (C): As illustrated in FIG. 11C, a Rapid Thermal Anneal (RTA) isconducted to crystallize the layers of polysilicon or amorphous silicondeposited in Step (B). Temperatures during this RTA could be as high as110° C. or more, and could even be as high as 800° C. The polysiliconregion obtained after Step (C) is indicated as 1110. Alternatively, alaser anneal could be conducted, either for all amorphous silicon orpolysilicon layers 1106 at the same time or layer by layer. Thethickness of the oxide layer 1104 would need to be optimized if thatprocess were conducted.Step (D): As illustrated in FIG. 11D, procedures similar to thosedescribed in FIG. 32E-H are utilized to construct the structure shown.The structure in FIG. 11D has multiple levels of junction-lesstransistor selectors for resistive memory devices. The resistance changememory is indicated as 1136 while its electrode and contact to the BL isindicated as 1140. The WL is indicated as 1132, while the SL isindicated as 1134. Gate dielectric of the junction-less transistor isindicated as 1126 while the gate electrode of the junction-lesstransistor is indicated as 1124, this gate electrode also serves as partof the WL 1132.Step (E): As illustrated in FIG. 11E, bit lines (indicated as BL 1138)are constructed. Contacts are then made to peripheral circuits andvarious parts of the memory array as described in embodiments describedpreviously.

FIG. 12A-F show another embodiment of the current invention, wherepolysilicon junction-less transistors are used to form a 3Dresistance-based memory. The utilized junction-less transistors can haveeither positive or negative threshold voltages. The process may includethe following steps occurring in sequence:

Step (A): As illustrated in FIG. 12A, a layer of silicon dioxide 1204 isdeposited or grown above a silicon substrate without circuits 1202.

Step (B): As illustrated in FIG. 12B, multiple layers of n+ dopedamorphous silicon or polysilicon 1206 are deposited with layers ofsilicon dioxide 1208 in between. The amorphous silicon or polysiliconlayers 1206 could be deposited using a chemical vapor depositionprocess, such as LPCVD or PECVD.Step (C): As illustrated in FIG. 12C, a Rapid Thermal Anneal (RTA) orstandard anneal is conducted to crystallize the layers of polysilicon oramorphous silicon deposited in Step (B). Temperatures during this RTAcould be as high as 700° C. or more, and could even be as high as 1400°C. The polysilicon region obtained after Step (C) is indicated as 1210.Since there are no circuits under these layers of polysilicon, very hightemperatures (such as, for example, 1400° C.) can be used for the annealprocess, leading to very good quality polysilicon with few grainboundaries and very high mobilities approaching those of single crystalsilicon. Alternatively, a laser anneal could be conducted, either forall amorphous silicon or polysilicon layers 1206 at the same time orlayer by layer at different times.Step (D): This is illustrated in FIG. 12D. Procedures similar to thosedescribed in FIG. 32E-H are utilized to get the structure shown in FIG.12D that has multiple levels of junction-less transistor selectors forresistive memory devices. The resistance change memory is indicated as1236 while its electrode and contact to the BL is indicated as 1240. TheWL is indicated as 1232, while the SL is indicated as 1234. Gatedielectric of the junction-less transistor is indicated as 1226 whilethe gate electrode of the junction-less transistor is indicated as 1224,this gate electrode also serves as part of the WL 1232.Step (E): This is illustrated in FIG. 12E. Bit lines (indicated as BL1238) are constructed. Contacts are then made to peripheral circuits andvarious parts of the memory array as described in embodiments describedpreviously.

Step (F): Using procedures described in Section 1 and Section 2 of thispatent application, peripheral circuits 1298 (with transistors andwires) could be formed well aligned to the multiple memory layers shownin Step (E). For the periphery, one could use the process flow shown inSection 2 where replacement gate processing is used, or one could usesub-400° C. processed transistors such as junction-less transistors orrecessed channel transistors. Alternatively, one could use laser annealsfor peripheral transistors' source-drain processing. Various otherprocedures described in Section 1 and Section 2 could also be used.Connections can then be formed between the multiple memory layers andperipheral circuits. By proper choice of materials for memory layertransistors and memory layer wires (e.g., by using tungsten and othermaterials that withstand high temperature processing for wiring), evenstandard transistors processed at high temperatures (>1000° C.) for theperiphery could be used.

Some embodiments of the invention may include alternative techniques tobuild IC (Integrated Circuit) devices including techniques and methodsto construct 3D IC systems. Some embodiments of the invention may enabledevice solutions with far less power consumption than prior art. Thedevice solutions could be very useful for the growing application ofmobile electronic devices and mobile systems such as, for example,mobile phones, smart phone, and cameras, those mobile systems may alsoconnect to the internet. For example, incorporating the 3D ICsemiconductor devices according to some embodiments of the inventionwithin the mobile electronic devices and mobile systems could providesuperior mobile units that could operate much more efficiently and for amuch longer time than with prior art technology.

Smart mobile systems may be greatly enhanced by complex electronics at alimited power budget. The 3D technology described in the multipleembodiments of the invention would allow the construction of low powerhigh complexity mobile electronic systems. For example, it would bepossible to integrate into a small form function a complex logic circuitwith high density high speed memory utilizing some of the 3D DRAMembodiments of the invention and add some non-volatile 3D NAND chargetrap or RRAM described in some embodiments of the invention. Mobilesystem applications of the 3DIC technology described herein may be foundat least in FIG. 156 of U.S. Pat. No. 8,273,610, the contents of whichare incorporated by reference.

In this document, the connection made between layers of, generallysingle crystal, transistors, which may be variously named for example asthermal contacts and vias, Thru Layer Via (TLV), TSV (Thru Silicon Via),may be made and include electrically and thermally conducting materialor may be made and include an electrically non-conducting but thermallyconducting material or materials. A device or method may includeformation of both of these types of connections, or just one type. Byvarying the size, number, composition, placement, shape, or depth ofthese connection structures, the coefficient of thermal expansionexhibited by a layer or layers may be tailored to a desired value. Forexample, the coefficient of thermal expansion of the second layer oftransistors may be tailored to substantially match the coefficient ofthermal expansion of the first layer, or base layer of transistors,which may include its (first layer) interconnect layers.

Base wafers or substrates, or acceptor wafers or substrates, or targetwafers substrates herein may be substantially comprised of a crystallinematerial, for example, mono-crystalline silicon or germanium, or may bean engineered substrate/wafer such as, for example, an SOI (Silicon onInsulator) wafer or GeOI (Germanium on Insulator) substrate.

It will also be appreciated by persons of ordinary skill in the art thatthe invention is not limited to what has been particularly shown anddescribed hereinabove. For example, drawings or illustrations may notshow n or p wells for clarity in illustration. Moreover, transistorchannels illustrated or discussed herein may include dopedsemiconductors, but may instead include undoped semiconductor material.Further, any transferred layer or donor substrate or wafer preparationillustrated or discussed herein may include one or more undoped regionsor layers of semiconductor material. Rather, the scope of the inventionincludes both combinations and sub-combinations of the various featuresdescribed hereinabove as well as modifications and variations whichwould occur to such skilled persons upon reading the foregoingdescription. Thus the invention is to be limited only by the appendedclaims

We claim:
 1. A semiconductor device, the device comprising: a firstsilicon layer comprising a first single crystal silicon; a first metallayer disposed over said first silicon layer; a second metal layerdisposed over said first metal layer; a first level comprising aplurality of transistors, said first level disposed over said secondmetal layer, wherein said plurality of transistors comprise a secondsingle crystal silicon; a third metal layer disposed over said firstlevel; a fourth metal layer disposed over said third metal layer,wherein said fourth metal layer is aligned to said first metal layerwith a less than 40 nm alignment error; and a via disposed through saidfirst level, wherein said first level thickness is less than twomicrons.
 2. The device according to claim 1, wherein said via comprisestungsten.
 3. The device according to claim 1, wherein said via has adiameter of less than 450 nm.
 4. The device according to claim 1,further comprising: connection pads disposed over portions of saidfourth metal layer, wherein said connection pads are capable to compriseconnections to external devices.
 5. The device according to claim 1,further comprising: a global power distribution network and a localpower distribution network, wherein said global power distributionnetwork comprises said fourth metal layer, and wherein said local powerdistribution network comprises said third metal layer.
 6. The deviceaccording to claim 1, wherein at least one of said plurality oftransistors comprises a two sided gate.
 7. The device according to claim1, further comprising: oxide to oxide bonds.
 8. A semiconductor device,the device comprising: a first silicon layer comprising first singlecrystal silicon; a first metal layer disposed over said first siliconlayer; a second metal layer disposed over said first metal layer; afirst level comprising a plurality of transistors, said first leveldisposed over said second metal layer, wherein said plurality oftransistors comprise second single crystal silicon; a third metal layerdisposed over said first level; a fourth metal layer disposed over saidthird metal layer, wherein said fourth metal layer is aligned to saidfirst metal layer with a less than 40 nm alignment error; a via disposedthrough said first level; and connection pads disposed over a portion ofsaid fourth metal layer, wherein said connection pads are capable tocomprise connection to external devices.
 9. The device according toclaim 8, wherein said via has a diameter of less than 450 nm.
 10. Thedevice according to claim 8, wherein said first level has a thickness ofless than two microns.
 11. The device according to claim 8, wherein saidvia comprises tungsten.
 12. The device according to claim 8, furthercomprising: a global power distribution network and a local powerdistribution network wherein said global power distribution networkcomprises said fourth metal layer, and wherein said local powerdistribution network comprises said third metal layer.
 13. The deviceaccording to claim 8, wherein at least one of said plurality oftransistors comprises a two sided gate.
 14. The device according toclaim 8, further comprising: oxide to oxide bonds.
 15. A semiconductordevice, the device comprising: a first silicon layer comprising firstsingle crystal silicon; a first metal layer disposed over said firstsilicon layer; a second metal layer disposed over said first metallayer; a first level comprising a plurality of transistors, said firstlevel disposed over said second metal layer, wherein said plurality oftransistors comprise second single crystal silicon; a third metal layerdisposed over said first level; a fourth metal layer disposed over saidthird metal layer, wherein said fourth metal layer is aligned to saidfirst metal layer with a less than 40 nm alignment error; a powerdistribution network, wherein said power distribution network comprisessaid third metal layer, and a plurality of connection paths from saidpower distribution network to said plurality of transistors.
 16. Thedevice according to claim 15, further comprising: a via disposed throughsaid first level, wherein said via comprises tungsten.
 17. The deviceaccording to claim 15, wherein said first level has a thickness of lessthan two microns.
 18. The device according to claim 15, furthercomprising: connection pads disposed over said fourth metal layer,wherein said connection pads are capable to comprise connection toexternal devices.
 19. The device according to claim 15, wherein at leastone of said plurality of transistors comprise a two sided gate.
 20. Thedevice according to claim 15, further comprising: a via through saidfirst level, wherein said via has a diameter of less than 450 nm.